The Ministry of Health and Welfare of Japan is planning a pooling system for multiple-choice questions (MCQs) for the national examination for medical practitioners. To clarify possible problems of such a system, a field study was performed by 10 medical schools in Japan using 90 MCQs from previous examinations. Nine hundred twenty-four 6th-year students participated in the field test. For each MCQ, the correct-response rates at the originating school and those obtained in the field test were significantly correlated. Thus, the correct-response rates to questions on the field test could be predicted from the rates at the originating schools. However, for each question the correct-response rate was significantly higher for students of the originating school than for students of other schools. In the national examination, care should be taken to prevent differences in scores on the basis of question sources.