Scopolamine dose-dependently inhibits passive avoidance latency and decreases spontaneous alternation in the Y-maze, suggesting effects on long-term and short-term memory, respectively. Chlorisondamine (10 mg/kg), a compound which produces a long-lasting central nicotinic receptor blockade, did not affect short-term and long-term memory performance. In normal rats, nicotine at the doses of 0.3, 1.0, and 3.0 mg/kg administered once had a facilitating effect on short-term memory; a higher dose (3.0 mg/kg) did not show a more pronounced effect than a lower one (0.3 mg/kg). Nicotine, by activating the nicotinic acetylcholine receptors, attenuated the impairment of short-term memory induced by muscarinic or dopamine D2 receptor blockade. On long-term memory, a single dose of nicotine (0.3, 1.0, 3.0 mg/kg) did not affect memory performance, but improved it after chronic (10 consecutive days, 0.3 mg/kg) administration. The antiamnesic effect of nicotine administered once was observed in scopolamine-, scopolamine+chlorisondamine- or sulpiride-treated rats. These results suggest that the antiamnesic effect of nicotine can result from an action at nicotinic receptors subtypes not blocked by chlorisondamine or at nonnicotinic receptors.