The metabolic fate of 1-(4-methoxy-6-methyl-2-pyrimidinyl)-3-methyl-5-methoxy-pyrazole (mepirizole, DA-398) was investigated in rat and rabbit. Four metabolites were isolated as crystals from the urine of medicated rats and identified as 1-(4-methoxy-5-hydroxy-6-methyl-2-pyrimidinyl)-3-methyl-5-methoxypyrazole (UNM-1), 1-(4-methoxy-6-methyl-2-pyrimidinyl)-3-hydroxymethyl-5-methoxypyrazole (UNM-2), 1-(4-methoxy-6-methyl-2-pyrimidinyl)-5-methoxypyrazole-3-carboxylic acid (UAM-1) and 1-(4-methoxy-6-methyl-2-pyrimidinyl)-3-methyl-4-hydroxy-5-methoxypyrazole sulfate (URM-1). From the rabbit urine, UAM, UNM-2, UNM-4 (1-(4-methoxy-6-hydroxymethyl-2-pyrimidinyl)-3-methyl-5-methoxypyrazole) were isolated and the excretion of UNM-1, UNM-3 (2-hydroxy-4-methoxy-6-methylpyrimidine) and UNM-5 (1-(4-methoxy-6-methyl-2-pyrimidinyl)-3-methyl-4-hydroxy-5-methoxypyrazole) were identified on thin-layer chromatogram. The major metabolite was UAM-1 both in rat and in rabbit.