1. From the urine of rats, rabbits and humans treated with noscapine, two novel metabolites were isolated and identified as 7-hydroxy-6-methoxyphthalide (MA-1) and 6-hydroxy-7-methoxyphthalide (MA-2), mainly by mass spectrometry. 2. MA-2 (free and conjugated) amounted to 8.5% dose in rats (n=2) and 1.7% dose in rabbits (n=2) during the first 48 h. In humans, MA-2 was excreted in amounts of 6.0 to 10.3% dose in the first 24 h urine (three men and a woman), although one woman excreted 52.5% dose as MA-2 during the same period. In all three species MA-2 was excreted 10 times more as conjugates than as the free metabolite. MA-1 was excreted only in trace amounts in the urines of three species. 3. In rabbits, the drug was metabolized also to 1-alpha-methyl-8-methoxy-6,7-dihydroxy-1-(6,7-dimethoxy-3-phthalidyl)-1,2,3,4-tetrahydroisoquinoline (4.6% dose, conjugated only) using g.l.c.-mass spectrometry. This metabolite was excreted conjugated at 0.6 to 5.2% dose in five human subjects, but was not detected in rats. 4. Three 0-demethylated metabolites of noscapine, previously reported, were determined using g.l.c.-mass spectrometry. The total demethylated metabolites (free and conjugated) amounted to 0.2%, 4.0% and 0.1-1.5% dose, respectively, in rats, rabbits and humans (n=5) in the first 24 h urine.