Tissues of kuruma shrimp Marsupenaeus japonicus Bate (5.7+/-1.1 g) reared in salinities of 18, 26, 34 and 42 were examined for levels of nucleotide-related compounds, ammonia, urea and uric acid, and activities of xanthine dehydrogenase (XDH), xanthine oxidase (XOD) and uricase. Levels of total nucleotide-related compounds, including xanthine and hypoxanthine, in gill increased directly with salinity, whereas these same levels in hepatopancreas were inversely related with salinity. Hemolymph ammonia, urea and uric acid levels, and epidermal ammonia, urea and uric acid levels increased directly with salinity, whereas hepatopancreas ammonia and uric acid and gill uric acid levels were inversely related to salinity. Activities of XDH and XOD in hepatopancreas increased directly with salinity level, whereas no significant difference of uricase activity in hepatopancreas was observed among the four salinities. It is concluded M. japonicus exhibited uricogenesis and uricolysis, and an increase of uricogenesis occurred for the shrimp under hyper-osmotic conditions (salinity of 42). Uric acid produced in the hepatopancreas was transported and accumulated in the epidermis, and removed along with the spongy connective tissue at the time of molting.