A computer-assisted self-instructional module was developed as a method of providing continuing education to pharmacists. A prospective, nonrandomized study was conducted to investigate the effectiveness of computer-assisted instruction (CAI). Using an Apple II microcomputer and anticoagulant therapy as the content base, a series of ten case studies was written and programmed. Twenty-two staff pharmacists from a university hospital and a community hospital participated. Participants were first given a pretest, proceeded through the CAI, took the same test as a posttest, then two weeks later, took a different posttest to measure knowledge retention. The mean test scores before and immediately after the CAI were 55.8% and 80.4%. The mean test score for the two-week posttest was 74%. The mean difference was found to be highly significant for both the pretest and immediate posttest (P less than 0.0001) and the pretest and two-week posttest (P less than 0.001). The study suggested that the use of a CAI module was effective in improving, as well as maintaining, pharmacists' knowledge and that a significant portion of knowledge gained was retained after a period of two weeks. Pharmacists' evaluations of this method of continuing education were generally favorable.