The effect of using a Personalized System of Instruction (PSI) method in teaching freshman biology in junior college and the relationship between biology achievement and selected variables were investigated. The sample of eighty freshmen was divided into two groups, experimental and control, and data were collected after one semester of treatment. Adjusted scores on the post-test were significantly different for the class using the PSI method. There was no significant difference between the sexes. Career motivation was the only significant factor between males and females. The significant predictors of biology achievement were college grade point average, treatment group, and the California Achievement Test composite score. The next group of predictors consisted of career motivation, fear motivation, and family size.