Cotinine, the main metabolite of nicotine, was administered intravenously to healthy male non-smoking volunteers in doses of 5, 10 and 20 mg, and orally in doses of 10 and 20 mg. Intravenous administration was characterized by a dose-independent half-life of 12.2 h, mean residence time of 15.9 h, total clearance of 3.64 l h-1 and a volume of distribution of 56.5 l. Renal clearance was 0.46 l h-1 and approximately 12.0% of the dose was excreted unchanged in the urine. The mean absorption time after oral dosing ranged between 1 and 3 h, the peak concentration was reached within 45 min and the mean elimination half-lives were 12.9 and 11.7 h, respectively, after the 10 and 20 mg doses. Systemic bioavailability ranged between 0.84 and 1.11 following 10 mg and between 0.97 and 1.03 following the 20 mg dose. Mean urinary recovery and renal clearance were almost identical with the values after iv administration.