Michael R. Bloomberg, the billionaire and former New York City mayor, is giving $600 million to the country’s four historically Black medical schools, which account for a significant percentage of all medical degrees awarded to Black doctors.

Through his charitable organization, Bloomberg Philanthropies, Mr. Bloomberg is giving $175 million each to Meharry Medical College in Nashville, Morehouse School of Medicine in Atlanta and Howard University College of Medicine in Washington. These donations are believed to be the largest ever to any single H.B.C.U., surpassing the $100 million gift that Spelman College in Atlanta announced in January.

The foundation is also giving $75 million to Charles R. Drew University of Medicine and Science in Los Angeles and an additional $5 million to help start a new medical school at Xavier University of Louisiana in New Orleans.

Dr. James E.K. Hildreth, president and chief executive of Meharry Medical College, said in an interview that the gift was “just a major, major investment that will have generational impact.”

The money is targeted at the medical schools’ endowments, which an announcement on Tuesday morning described as “significantly underfunded” as a result of entrenched discrimination and lagging federal and state support.

Despite their small number, the historically Black medical schools are strong engines of social mobility for their graduates, and contributors to the well-being of Black communities, research shows.

Only about 5 percent of U.S. doctors are Black, according to a 2022 report from the Association of American Medical Colleges. But H.B.C.U.s play an outsize role in their education. Graduates of historically Black colleges and universities account for half of the country’s Black doctors, according to the United Negro College Fund. And in 2021-22, 10 percent of medical degrees to Black graduates were awarded by H.B.C.U.s, according to federal data.

Mr. Bloomberg’s donation comes as medical schools are grappling with a new and possibly more forbidding environment around the quest for a diverse student body. The Supreme Court has banned race-conscious admissions, a move that could further influence who is admitted to medical school, especially elite medical schools.

And at least three medical schools — New York University, Albert Einstein College of Medicine and Johns Hopkins University (in an initiative funded by Mr. Bloomberg in July) — have instituted free tuition for most or all students. There is some evidence that free tuition, while intended to provide more opportunity for lower-income students, can drive medical school admissions to become more competitive, in turn making them less diverse.

“We have much more to do to build a country where every person, regardless of race, has equal access to quality health care, and where students from all backgrounds can pursue their dreams,” Mr. Bloomberg said in a statement.

The donation aims, in a sense, to right a historic blow to Black medical education. The Flexner Report of 1910, an exposé of medical education in general, led to the closing of five of the seven historically Black medical schools then in existence. It recommended that only Meharry and Howard should survive. Ever since, there has been a struggle to increase the number of Black doctors, who are likely to go into Black communities to practice, and who research has shown achieve better outcomes for their Black patients.

“For decades after that, most of the Black doctors in this country came out of Howard and Meharry,” Dr. Hildreth said. “African Americans were being excluded for the most part from white schools in the South, and they were looking to Meharry in particular for their training. It’s a legacy on one hand we’re proud of. On the other hand, it’s not a happy one for the country, I think.”

This is not Mr. Bloomberg’s first contribution to H.B.C.U.s. In September 2020, his Greenwood Initiative announced a $100 million gift to the four H.B.C.U. medical schools to reduce student debt.

Dr. Hildreth said the four college presidents had learned of Mr. Bloomberg’s newer, bigger gift last week at a gathering to celebrate his 2020 gift to them. He said he was excited that “it shows the rest of the country and the world” that Mr. Bloomberg and his philanthropic organization value H.B.C.U.s.

The United States has a long lineage of H.B.C.U.s The first, now Cheyney University of Pennsylvania, was founded in 1837, before schools such as the University of California and Cornell University. But there has been limited financial support for them.

Even though government funding is the most substantial revenue source for H.B.C.U.s, the schools generally receive far less money than other institutions. Last year, the federal government sent letters to 16 governors, complaining that in recent decades their states had severely and illegally underfunded H.B.C.U.s. The cumulative toll, the Biden administration said, approached $13 billion.

And the United Negro College Fund, in a report released in January, noted that no H.B.C.U. had an endowment valued at $1 billion or more, a threshold exceeded by more than 100 schools in the United States. Most H.B.C.U.s were working with less than $100 million, according to the fund.

Still, since the 2020 murder of George Floyd in Minneapolis, H.B.C.U.s have enjoyed a surge of enormous gifts.

In January, the Lilly Endowment announced it would give the United Negro College Fund $100 million. The college fund said that the money would add $2.7 million to each of its 37 members’ endowments — a sum that it said doubled the value of some schools’ accounts.

A week later, Spelman announced its $100 million gift from the billionaire couple Ronda Stryker and William Johnston. Some $75 million, the college said, would be used for endowed scholarships, with the rest dedicated to priorities like student housing and the development of what the college described as “an academic focus on public policy and democracy.”

There have been other head-turning donations, too. After her divorce from the Amazon founder Jeff Bezos, MacKenzie Scott poured more than $500 million into H.B.C.U.s. And four years ago, after Mr. Floyd’s death, the Netflix co-founder Reed Hastings and his wife, Patty Quillin, spread $120 million among the college fund, Spelman and Morehouse.

The gifts announced on Tuesday, along with the affirmative action decision, could spur some students of color seeking a “more welcoming, supportive” environment to apply to H.B.C.U.s, Dr. Hildreth said.

“I think it could have an impact on enrollment, and that needs to be matched with investments,” he added. “That’s the reason we’re so excited about this.”