Unis is a nurse expert system prototype specifically designed to assist nurses caring for elderly, incontinent patients residing in nursing homes. Two studies measuring the performance level of UNIS were implemented. In the first study, results of sessions with UNIS on case studies of elderly, incontinent patients were compared to sessions with nurse experts. The relevance of questions, value of recommendations and overall performance were rated by an evaluation panel. In the second study, UNIS was implemented on two nursing units in a nursing home. The number of wet occurrences of patients residing on units where UNIS was consulted by nurses was compared to the number of wet occurrences of patients residing on units where UNIS was not consulted by nurses. The knowledge of urinary incontinence of nurses who consulted UNIS and those who did not consult UNIS were also compared. The results indicate that when judged by an evaluation panel, the relevance of the questions and value of the recommendations generated by UNIS were not rated significantly different than ratings assigned to nurse experts consulting on the same case studies. There was a significant difference between assigned ratings for overall performance; F.01 (4,16) = 10.4. UNIS scored the highest on four out of five case studies. In the second study, the number of wet occurrences of patients residing on units where nurses consulted UNIS decreased significantly; F.01 (2,9) = 34.67. The knowledge of urinary incontinence also improved significantly when nurses' consulted UNIS; F.001 (2,157) = 19.46. The methods and results of these two studies are presented.