Albendazole, a new broad spectrum benzimidazole anthelmintic, has been administered in 10 male volunteers. Administration was randomized using 100 mg tablets, 200 mg tablets and a 2% suspension. Blood samples were obtained 0.5; 1; 1.5; 2; 2.5; 3; 3.5; 4; 5; 6; 8; 12; 24; 72 h after treatment. Albendazole sulfoxide, one of the mains albendazole blood metabolites, was assayed by HPLC and the blood half life was calculated as 8 1/2 h. The three different pharmaceutical formulations were considered bioequivalent. Urines were collected, and using T. L. C. Technics, main metabolites were identified and characterized. Hydrolysis of the carbamate function and oxidation of the sulfur atom, the alkyle chain and the aromatic ring were the main biotransformations observed.