Two species of amphipods were exposed to two differen tributyltin compounds. Both compounds were acutely toxic in 10 days at concentrations of 10 ppb and above. In another set of experiments Gammararus oceanicus from the Baltic Sea were exposed to tributyltin leachate from panels painted with two different antifouling paint formulations. One type of paint leached tributyltin about 10 times faster than the other. Increase on painted surface are and leaching rate were both directly correlated with amphipod mortality in short-term tests. Measured tributyltin concentration, with final leachate concentraton of 4.8 ppb caused total mortality in 5 days. The results of these experiments show that tributyltin compounds are very toxic to some non-target organisms. Thus the intelligent choice of antibiofouling paint formulations depends upon an acceptable comproimise between leachates, which are effective at the painted surface but which minimize effects on non-target organisms