Diethyldithiocarbamate (DDC) and fusaric acid (FA), administered immediately posttraining, disrupted retention performance of rats trained on a one-trial inhibitory avoidance task. Posttraining DDC disrupted retention performance if the treatment was delayed up to at least 24 h (but not 72 h) after training. A single DDC injection also disrupted retention performance if the treatment was administered up to 10 days prior to training. The effects of DDC and FA upon several neurobiological measures were also investigated. Amnestic doses of DDC influence brain and adrenal catecholamine levels, brain electrographic activity and hippocampal Timm's staining. On the other hand, amnestic doses of FA only affected catecholamine levels. The amnestic effects of DDC were dissociated from brain seizure activity produced by DDC. The effects of DDC and FA upon retention may have been related to the drugs' effects upon catecholamine systems, but the bleaching by DDC of Timm's staining could reflect additional processes involved in DDC's effects upon retention. As opposed to the more widespread effects of DDC, FA's relative lack of effect upon other neurobiological measures more strongly supports a catecholaminergic interpretation for its effect upon retention.