A flow-through system was used to follow naphthalene and naphthalene metabolite accumulation in the seawater and in the tissue of the oyster Ostrea edulis. After 72 h, 82.5% of the naphthalene carbon was recovered from the system. Glucose was added to seawater to stimulate the pathways of glucose metabohsm in the oysters. Streptomycin (100 ppm) reduced microbial oxidation of naphthalene and glucose, and reduced bacterial growth. However, even in the presence of streptomycin, microbial oxidation of naphthalene was considerable. The main oxidation product recovered from seawater was 14CO2. Radioactivity was also associated with compounds which separated by TLC with 2-and 1-naphthol. The pattern of naphthalene uptake and accumulation in oyster tissues was relatively constant after only a few hours of exposure to naphthalene. The potential of tissues to accumulate naphthalene was shown to be a function of multiple variables such as nutritional state, lipid concentration, length of exposure to naphthalene, and the external naphthalene concentration. Carbon-14-1abeled metabolltes derived from 14C-naphthalene were consistently recovered from digests of the oyster tissues. Non-CO2 alkaline-soluble substances were the primary metabolltes. Hexane-extractable substances, which separated by TLC with known standards of 2-and 1-naphthol, were consistently recovered from seawater and tissue digests. It was not possible to conclude that these metabolites were a result of naphthalene metabolism by oyster enzyme systems.