Groups of estuarine clams, Rangia cuneata, were exposed for 24 hours to synthetic seawater containing in solution 0.0305 ppm benzo[a] pyrene-C14. In two experimental exposures, average total concentrations of benzo[a]pyrene (BAP) in the clam tissues were 7.2 ppm and 5.7 ppm, approximately 200 times above the ambient level. The majority of the radioactivity was localized in the viscera which contains the digestive system, gonads, and heart. The other tissues analyzed, the mantle, gills, adductor muscle, and foot, each contained 3–16% of the radioactivity. When returned to isotope-free seawater, the clams immediately began to release the accumulated BAP. After 30 days only 0.07 ppm BAP remained in the tissues. BAP could not be detected (limits of detection, 0.01 ppm) in clams maintained in isotope-free seawater for 58 days. During depuration, the distribution of radioactivity in the tissues remained relatively constant. The viscera contained most of the activity at all sampling times.