An AAPCC-designated poison center developed and validated an objective testing instrument to evaluate learning during a poison center clinical rotation for 2nd-year emergency medicine residents and 5th-year pharmacy students. The examination contained multiple-choice, true-false, and fill-in questions pertaining to basic clinical toxicology. A pretest was administered prior to the rotation and a post-test was administered upon completion of the rotation. Overall pre-test mean was 56.2%; physician pre-test mean was 73.8%, and student pre-test mean was 43.9%. Overall post-test mean was 78.7%; physician post-test mean was 85.7%, and student post-test mean was 81%. Pre-test scores ranged from 21 to 86% for the group, and post-test scores ranged from 68 to 96%. The mean difference in pre-test to post-test score was 26.9%. These data suggest that a poison center rotation can result in significant increases in post-test scores in comparison to pre-test scores.