An interactive microcomputer-videodisc programme for providing instruction in interpreting the peripheral blood smear was evaluated by 23 medical students. The mean scores of the students on a test of interpretation of photomicrographs of blood smears increased significantly after use of the teaching programme. The students' responses to a questionnaire indicated that they viewed computer based instruction as a useful learning tool. The results of the study suggest that computer assisted instruction may be one method for addressing some of the current problems in medical education.