The effects of mescaline hydrochloride (4.95-79.2 mg/kg i.p.) and its non-hallucinogenic analogue 3,4-dimethoxyphenylethylamine hydrochloride (DMPEA) (12.5-100 mg/kg i.p.) on shock avoidance in a shuttlebox were studied in male Long-Evans rats trained to high (above 88%, good performers) or low (below 6%, poor performers) stable base-line avoidance rates. In good performers, mescaline and DMPEA caused a dose-dependent decrease in avoidance rate (ED 50's 44.6 and 39.2 mg/kg, respectively) without affecting presession (5-min adaptation period) or intertrial shuttlebox crossings. In poor performers, mescaline caused a dose-dependent increase in avoidance rate (ED 50 = 24.8 mg/kg) and intertrial crossings, without affecting presession crossings. The results suggest that mescaline, but not DMPEA, has dual facilitative and disruptive effects on avoidance behavior at similar dose ranges. The facilitative, but not the disruptive, effect may be related to changes in motor activity.