The attrition rate of 5% to 50% from US medical schools in the 1920s propelled the development of a test that would measure aptitude for medical studies. Since its development in 1928, the Medical College Admission Test (MCAT) has undergone 5 revisions. The first version was divided into 6 to 8 subtests that focused on memory, knowledge of scientific terminology, reading and comprehension, and logic. The second, which appeared in 1946, was reduced to 4 categories: verbal and quantitative skills, science knowledge, and added a category called understanding modern society. The major difference in the third version, launched in 1962, expanded the test's understanding modern society section to a broader test of general information. In 1977, the MCAT underwent its fourth change: its science section, reading and quantitative skill assessment sections were expanded; its general liberal arts knowledge section was eliminated; its scoring report structure and scoring range were altered; and its cultural and social bias was minimized. The current version, beginning in 1991, has undergone another significant change. Although it does not contain independent measures of either liberal arts or numeracy as separate categories, quantitative skills are needed to solve some of the problems in biological and physical sciences. However, its principal innovation is the writing sample section. Through its 74-year history, the various renditions of the MCAT demonstrate that the definition of aptitude for medical education reflects the professional and social mores and values of the time.