The interpretation of peripheral blood smears has an important role in the diagnosis of hematologic diseases and is, therefore, part of the education of physicians and technologists. We describe a computer program, PeripheralBlood-Tutor (Lippincott-Raven, Philadelphia, Pa), that teaches the morphologic features of normal and abnormal peripheral blood smears; we also describe the evaluation of the effectiveness of the program in 133 second-year medical students who were required to use the program in their hematology course. The version of the PeripheralBlood-Tutor used in the study had 2 distinct but equivalent 20-question examinations; one examination, the pretest, was taken before the students viewed the contents of the program, and the other examination, the posttest, was taken after completing the program. The mean score on the pretest was 61% (SD, 14%), the mean on the posttest was 91% (SD, 10%), and the improvement was significant. In addition, 4 questions about peripheral blood smears, which were based on printed images, were administered at the end of the hematology course. The students scored an average of 2.75 (SD, 0.86), and a positive correlation was found between these scores and the scores on the Tutor posttest. The results of the study suggest that PeripheralBlood-Tutor is feasible to implement, and it helps students learn to interpret peripheral blood smears. The use of PeripheralBlood-Tutor is now a requirement in the medical school curriculum, the medical technology program, and the pathology residency at the University of Washington, Seattle.