The 8 patients involved in this study were impaired on tests assessing knowledge of objects and on the demonstration of their use. The patients' success in object use was significantly correlated with their knowledge about the objects, providing further evidence that conceptual knowledge plays a key role in object use. Having a recipient present improved performance in the moderately impaired patients, suggesting that a certain level of conceptual knowledge must remain for the additional information to be beneficial. Although overall accuracy in using the target objects was not related to our measures of affordance, the specific aspects of use afforded by the objects' structures were relatively impervious to semantic impairment, suggesting a role for affordance information when object-specific knowledge is disrupted. The patients' familiarity with the objects was an important predictor of performance. Finally, despite good performance on tests of mechanical problem solving, the patients showed very little evidence of employing these skills in their interactions with real objects.