The physiological response to nicotine topically applied to the skin was measured in an adult male volunteer. Nicotine base (9 mg) was applied in a 30% aqueous solution to intact skin on the underside of the forearm. Salivary nicotine, heart rate and blood pressure were monitored for 12 h after application of the nicotine. Within 30 min a significant level of nicotine was detected in the saliva (50 ng/ml), pulse had risen by 15 beats/min and systolic blood pressure had risen 10 mmHg. Nicotine levels remained elevated for 2 h and were comparable to levels of nicotine produced by cigarette smoking. Because previous research has shown nicotine to suppress smoking behavior, it may be fruitful to examine transdermal administration of nicotine as a smoking reduction and cessation aid.