This investigation had three purposes: (1) to document any immediate and continuing benefits associated with the use of microcomputer-administered testing; (2) to determine what type of student might benefit most from microcomputer-administered diagnostic testing; and (3) to document the feasibility of microcomputer-administered diagnostic testing. The subjects of the study were enrolled in a biology course based on the BSCS Blue text. A random half of the students received behaviorally-stated performance objectives, while the remaining half received behaviorally-stated performance objectives in conjunction with microcomputer-administered diagnostic testing. The results of this study indicate that microcomputer-administered diagnostic testing can positively influence the immediate, but not the continuing, achievement of students in science. In addition, neither student aptitude nor achievement motivation level were found to interact with treatment or influence achievement. Affective data indicate that students react favorably to the use of objectives, computers, and diagnostic testing. Cost summary data reveal that when the expense of administering diagnostic testing by microcomputer is prorated over a five-year period, the cost of a diagnostic test is reduced to approximately three cents.