Effects of chlordiazepoxide (CDP) were examined on the performance of rats in an eight-arm radial maze with four cued and food-baited arms. Two conditions were used; random, with cue location varying over trials, and constant, with the same subset of arms consistently cued. In rats pre-trained to a 60-70% efficiency level (Rewarded entries/Total entries X 100), the effects of CDP (2.5, 5.0 and 10.0 mg/kg, IP) differed according to condition. Efficiency was substantially reduced in the random condition, and types of error were undifferentiated. In the constant cue condition the post-drug drop in efficiency was less marked, and errors were selectively those of re-entry into rewarded arms. In both conditions there was a high incidence of error clusters involving re-entries into both rewarded and non-rewarded arms in the random condition, and rewarded arms in the constant condition. The results suggested that CDP induced a general disruption of information processing rather than a specific impairment of working memory, together with some response perseveration which could occur in the presence or absence of discrimination failure.