In a study of the development of measures that can assess specific learning and reasoning changes affected by a problem-based learning (PBL) curriculum in medical education, evidence is provided of the cognitive benefits of a PBL approach. To determine whether PBL students reach reasoning goals with a novel clinical case, the study evaluated directionality of reasoning, coherence of explanations, and use of basic science information in explanations for 20 medical students in a PBL class and 20 in the same core curriculum without the PBL experience. Both groups evaluated the same clinical case study. The paper-and-pencil measures that were developed revealed a significantly greater use of hypothesis-driven reasoning in the PBL group, as well as greater coherence in their explanations. PBL instruction appears to have distinct cognitive consequences that may influence medical practitioners throughout their careers and may shape the learning strategies they use in lifelong learning. Six figures present study data. (Contains 14 references.) (SLD)