Patas monkeys acquired a different four-response chain each session by responding sequentially on three levers in the presence of four discriminative stimuli (numerals). The response chain was maintained by food presentation under a fixed-ratio schedule. Errors produced a brief timeout but did not reset the chain. Each day there were four 15-min sessions, with a 10-min intersession interval. Cumulative dose-effect curves for phencyclidine were obtained by giving an IM injection before each of the four sessions; successive injections increased the cumulative dose by 1/4 log-unit steps. When phencyclidine was administered alone, overall response rate decreased and percent errors increased with increasing doses. When nicotine was administered alone (IM) before the first session, the higher doses initially produced large decreases in overall response rate. Unlike phencyclidine, nicotine alone generally had no effect on percent errors. When intermediate or high doses of phencyclidine were administered after pretreatment with certain doses of nicotine, both the rate-decreasing and error-increasing effects were smaller than those produced by phencyclidine alone. This attenuation of the disruptive effects of phencyclidine on acquisition occurred at a time when nicotine alone had little or no behavioral effect.