In the early summer of 1990, a survey of the wild Japanese oysters was conducted in relation to the organotin contamination from antifouling paints on recreational boat hulls in the waters of Aburatsubo Bay. No correlation was observed between the incidence of dead shell and the concentration regime of the main parent pollutant tributyltin (TBT) in the waters. The TBT concentrations in the oysters (111-653 ng/g wet weight) were among higher levels found in bivalves collected from various localities around Japan in the years up to 1990. The TBT body burdens were supposed to be inversely related to the ambient water concentration regimes in Aburatsubo Bay. Spat fall and the larger oysters observed in the innermost inlet waters with higher TBT concentration regimes and the higher TBT body burdens without shell deformation suggest that the natural population in the study area belongs to the different genetic race with higher TBT tolerance from the Japanese oyster cultured in Europe. Body burdens of the degradation products, dibutyltin (DBT) and monobutyltin (MBT), were not correlated with those of the parent pollutant TBT but with the TBT concentration regimes in the ambient water. An inference was made on the source of the DBT and MBT in the oysters, viz. the most plausible main source of DBT and MBT is the food including detritus. The triphenyltin (TPT) concentrations (4 to 18 ng/g wet weight) were considerably low among the levels found in bivalves collected from various localities around Japan. The body burdens of TPT and the primarily degradation product, diphenyltin (DPT), as well as those of DBT and MBT were seemingly correlated with the concentration regimes in the ambient water. The secondary product, monophenyltin (MPT), was not detected in all the samples examined.