The performance of practicing internists on the American Board of Internal Medicine's 1980 Recertification Examination was examined in two studies. In the first study, a psychometric common-item equating technique was used to compare the performance of 1980 recertification candidates with that of 1979 certification candidates. Results showed that the knowledge base of practicing internists was similar to that of residents completing training. The second study analyzed the performance of 1980 recertification candidates to determine whether being certified or having an interest in a subspecialty affects a physician's performance on items in that area. The results showed that subspecialists do significantly better than general internists on items pertaining to their area of specialization. Similar outcomes were found for internists with a special interest in a subspecialty area. These findings establish the importance of continued periodic evaluation and support the development of an evaluation tool tailored to the physician's area of concentration.