Frank Lappin Horsfall, Jr. (Seattle, December 14, 1906 – New York City, February 19, 1971) was an American microbiologist specializing in pathology.

He worked at the Rockefeller Institute, New York, from 1934 to 1960[1] and in the early 1950s ran the Virology Laboratory there.

[3] He was elected in 1948 a member of the United States National Academy of Sciences.

[5][6] He was the president of the American Association of Immunologists for the academic year 1967–1968.

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