Reported are results of a study that examined the relationships between university students' entry characteristics and achievement in biology. Variables judged most likely to be predictors of achievement were: (1) scholastic aptitude (quantitative and verbal); (2) level of cognitive development; (3) locus of control; (4) grade point average; (5) age; and (6) gender. Data on achievement variables were collected with the administration of four multiple-choice objective referenced tests. Data from over 1000 students in introductory biology at the University of Georgia were examined by using regression analysis and general linear model procedures with SAS computer programs. Results included the finding that on all the biology achievement measures, the SAT (quantitative) score was the single best predictor of achievement, while the second best predictor was level of cognitive development. Implications are discussed regarding the improvement of postsecondary science instruction. (CS)