The urinary pattern of pyrithione metabolites in urine of the rat, rabbit and rhesus monkey was similar to that of the swine after iv. administration of sodium pyrithione (Sodium Omadine) and the magnesium sulfate adduct of 2,2'-dithio-bis(pyridine-1-oxide), (Omadine MDS). The major metabolite accounting for 80% or more of the metabolites in urine was the S-glucuronide of 2-mercaptopyridine-N-oxide. After Omadine MDS administration, three transient metabolites and one persistent metabolite were observed in the plasma. The transient metabolites were tentatively identified as 2-methylthiopyridine-N-oxide, 2-methylsulfinylpyridine and 2-methylsulfinylpyridine-N-oxide. 2-Methylsulfonylpyridine was the only metabolite observed in the plasma 16 hr after Omadine administration. This metabolite could be detected 14 days after rats were treated repeatedly with a shampoo formulation containing Omadine MDS.