In the 1988 study reported here, Medical College Admissions test (MCAT) scores and grade point averages for undergraduate science courses (S-GPAs) were examined for predictive validity and differential prediction of National Board of Medical Examiners Part I scores. Data from 579 medical students from the classes of 1979-80 through 1983-84 attending a midwestern medical college were analyzed via moderated multiple regression. The findings indicated that using the S-GPA and a composite MCAT score based on the Biology Knowledge, Chemistry Knowledge, Physics Knowledge, Science Problems, and Reading subtests was valid and equally predictive for the minority and majority groups studied. These results are discussed in terms of past findings on cognitive tests in general, and the MCAT and the S-GPA specifically.