Abstract: Methimidol 1-(2′-hydroxylethyl)-2-methylimidazol hydrochloride is a new oral drug for treatment of leptospirosis. It has been designed and synthesized by our laboratory since 1970.Both in vitro and in vivo experiments showed that "methimidol" is an antileptospiral drug with high efficacy and relatiyely low toxicity.After oral administration, "Methimidol" is absorbed quickly and completely from the gastro-intestinal tract and excreted mainly from kidney. It is distributed through blood stream to all tissues, but chiefly in liver and kidney.After the successful treatment of experimental leptospiral infection in animals, 281 cases of leptospiral infection in man were treated with the drug with a cure rate of 94.31%. No Herxheimer reaction occurred as after penicillin therapy. This drug can be orally administered and is fairly effective with no significant side effects.