Purpose. To explore the degree of retention of pharmacologic knowledge of third-year medical students taught in a new pharmacology teaching program. Method. In 1997, the authors administered a retention test consisting Of 100 Multiple-choice questions, each with only one correct answer, to 457 third-year medical students at the National University of Mexico. Students were not told in advance about this diagnostic evaluation, which was given eight months after they completed the second-year pharmacology course. As a comparison, the authors also analyzed the results obtained by the same students in the three partial examinations taken during the second-year pharmacology course. The Kolmogorov-Smirnov procedure and Wilcoxon and chi-square tests were used to analyze data. Results. The distribution of scores obtained in the partial exams well approximated a symmetrical bell-shaped curve, and the mean score was 59,9%. In contrast, in the retention test the distribution was negatively skewed, the mean score (69.8%) was significantly higher (p < .001), and the curve was clearly displaced to the right of that corresponding to the partial exams. The percentage of students obtaining at least a passing score (60%) was considerably higher for the retention test (82.5 versus 51.9). Conclusion. These findings, indicating that medical students taught in a new pharmacology program developed adequate basic pharmacologic knowledge, should encourage other medical schools to formally evaluate their teaching programs and continue efforts to improve pharmacologic education of medical students.