BOF-4272 (+/-)-8-(3-methoxy-4-phenylsulphinylphenyl) pyrazolo[1,5-a]-1,3,5-triazine-4-(1H)-one, a new synthetic anti-hyperuricaemic drug, which has a chiral centre and exists as racemates, is a potent inhibitor of xanthine oxidase/dehydrogenase in the purine catabolism pathways. The present studies using mice demonstrated that BOF-4272 was specifically distributed in the liver, which is the main organ of uric acid production. Therefore, a decrease in uric acid concentration in the liver, rather than the plasma, was identified as a pharmacological action of BOF-4272. The ratio of liver to plasma concentrations of BOF-4272 increased from 2.5 to 6.3 over time, up to 8 h after oral administration. The elimination half-life of BOF-4272 in the liver was 5-1-fold longer than that in the plasma. High concentrations of BOF-4272 were observed in the liver up to 8 h after oral administration. Furthermore, the influx of BOF-4272 into hepatocytes occurred in a temperature-dependent manner. The liver concentrations of uric acid from 1 h to 8 h after the oral administration of BOF-4272 (0.34-0.75 microg (g tissue)(-1)) were significantly lower than those in control animals (5.03-10.96 microg (g tissue)(-1)). BOF-4269 (the sulphide metabolite of BOF-4272) was the only metabolite detected in plasma or faeces after intravenous or oral administration. BOF-4269, which has no inhibitory action on the uric acid biosynthesis system, is generated by the metabolism of BOF-4272 in the intestinal tract. In conclusion, this work using the liver as the target organ has allowed us to identify the pharmacological actions of BOF-4272 in mice. The long-lasting effect of BOF-4272 in reducing levels of hepatic uric acid was consistent with the prolonged high BOF-4272 concentrations in the liver. These results also demonstrate that the mouse is a suitable animal species for evaluating the clinical pharmacology and pharmacokinetics of BOF-4272.