The purpose of the study reported here was to compare two teaching formats, the traditional lecture and the case presentation, to determine which technique is more effective in continuing medical education (CME). Effectiveness was measured by assessing pediatricians' cognitive knowledge utilizing preinstruction and postinstruction multiple-choice tests, the physicians' performances using simulated patients, and the physicians' office records on diagnoses and treatment plans. There were differences between the two teaching techniques in regard to their impact on physicians' knowledge and their performance with patients. Physicians attending case presentation sessions were more likely to increase their cognitive knowledge than physicians attending the lecture sessions, but retention of knowledge was only slightly higher for the case presentation group than the lecture group. More simulated mothers making visits to the offices of pediatricians who had been in the case presentation group reported feeling that the physicians' plans for their children were totally or partially appropriate than did mothers visiting pediatricians from the lecture group. There were few correlations between the physicians' cognitive knowledge and their performances. Based on the findings of the study, recommendations are suggested for use in planning CME.