1. The metabolism of noscapine was studied in rabbits, rats and human. 2. Apart from the O-demethylated metabolites already reported, three metabolites were isolated and identified as meconine, cotarnine and hydrocotamine, respectively. 3. Mass fragmentography (chemical ionization) was used to determine these products simultaneously. 4. Meconine was the major metabolite in all three species, accounting for about 3, 8 and 2% of the dose in the first 24 h urines of rats, rabbits and humans, respectively, although one woman excreted to a very high extent (22%). In rats, cotarnine bases were excreted at almost same level as that of meconine, but at lesser extent in other two species. Hydrocotamine and unchanged noscapine were excreted to less than 1% dose.