In the first study to examine direct nicotinic augmentation of central cholinergic functioning in Alzheimer's disease, six patients were studied in an intensive pilot study with three doses (0.125, 0.25, and 0.5 microgram/kg/min) of intravenous nicotine and placebo. Cognitive tests showed a decrease in intrusion errors on the middle (0.25 microgram) dose. Prominent behavioral effects were noted, with significant dose-related increases in anxiety and depressive affect. These results suggest that central nicotinic cholinergic stimulation deserves further investigation as a treatment in Alzheimer's disease and that nicotine may also be a useful investigative tool in other populations as a probe of central cholinergic function, especially in regard to the modulation of affect.