Investigated auditory word discrimination skill in children diagnosed as having minimal brain dysfunction (MBD), a heretofore unexplored topic in the study of MBD. A lack of auditory discrimination skill seems relevant to learning deficiency in language acquisition, a typical sign of MBD. The present study tested the hypothesis that phonemic aural discriminations would be difficult to make for boys diagnosed as having MBD. Errors and nonresponses made while Ss performed an extended auditory word discrimination task were compared between a group of 26 boys diagnosed as having MBD and a matched normal group. As expected, the MBD group had a significantly higher error rate than the normal group even when Ss were discriminating easy word pairs composed of dissimilar items (e.g., reading, math). These and other results suggested that the MBD group was very susceptible to fatigue even while motivated to perform well and while able to improve with practice. The relatively inferior performance of the MBD group was interpreted as resulting directly from a lack of auditory discrimination skill and indirectly from fatigue and its accompanying attention loss.