This paper deals with the bioconcentration of 14C-simetryne from water by aquatic test organisms: green algae-Monoraphidium minutum, rotifers-Brachiomus rubens, daphnids-Daphnia magna, and fish-Brachydanio rerio. The chemical was bioconcentrated rapidly in all test species during the first 48 hours of experiment. The BCF values (bioconcentration factor) from all uptake studies show that simetryne has higher accumulation in algae than in rotifers, daphnids and zebra fish. The logarithm of the n-octanol/water partition coefficient of simetryne measured as 2.06 .+-. 0.05 was correlated with the BCFs in the organisms as based on the lipid contents. 14C-simetryne uptake via the food-chain amounted to only 22% to 42% of the bioconcentration from water. Clearance of 14C-derived residues from fish was rapid with a half-life of 2.1 days.