Thirty aphasic subjects were asked to point to pictures on auditory command both when the distractors came from the same semantic category as the target and when the distractors were unrelated to the target picture. The aphasics made significantly more semantic errors than non-aphasic brain-damaged controls; the incidence of semantic comprehension errors was unrelated to aphasic diagnostic groups but was related to the overall severity of aphasia. The subjects were subsequently asked to name the pictures from the comprehension task; pictures that had elicited semantic errors in comprehension were no less likely to be named than those that had not, but the incidence of semantic errors in comprehension correlated significantly with their incidence in naming. The implications of a semantic deficit common to both auditory comprehension and naming that is not specific to particular lexical items is discussed in relation to a number of information processing models of the lexicon.