This study compared the effectiveness of three sequences of prerequisite courses required before taking zoology. Sequence 1 prerequisite courses consisted of general biology and human biology; Sequence 2 consisted of general biology; and Sequence 3 required cell biology. Zoology students in the spring of 1972 were pretest and a posttest. The mean difference scores on these tests were compared for all three sequences by using the t-test at the .05 confidence level. Correlation coefficient were determined for SAT scores and zoology final examination percent score, zoology final examination percent score and zoology final grade, final grades in prerequisite courses, and final grade in zoology for all the sequences. Zoology final examination items were categorized, and the bias of the examination was determined. Students were characterized with respect to level and orientation of their subsequent biology courses and their attitudes and reasoning abilities. The study found no significant relationships between performance in zoology and performance in prerequisite courses of the three sequences. (Author/BR)