The fate of ring-14C labeled triphenyltin hydroxide was studied in a model ecosystem consisting of soiI, water, and channel catfish (Ictalurus punctatus). Two initial levels of triphenyltin hydroxide concentration in soiI, 1.0 and 0.010 ppm, were compared. The soiI showed a gradual loss of 20 to 30% of the total 14C residues. Only about 33% of the remaining soil residues could be extracted and almost all of these were triphenyltin hydroxide. Total residues in the water were very low. Catfish muscle and viscera accumulated 14C residues continually throughout the treatment portion of the experiment. When the catfish were transferred to untreated aquaria the total residues in the catfish remained at a steady plateau. In the catfish muscle, extractable residues accounted for less than 10% of the total residues and essentially all were triphenyltin hydroxide. Approximately 80% of the total residues in the entire model ecosystem remained bound, mainly in the soiI and catfish. Of the extractable residues from the soiI, water, and catfish muscle the greatest percentage was found to be triphenyltin hydroxide.