Embryolarval lethal effects of Mexel 432, an antifouling agent, were determined in the laboratory during continuous exposure, beginning at fertilization, under various experimental conditions in eight different spawns of the common carp (Cyprinus carpio L). In synthetic water at 24 degrees C and without larval feeding, correlations between LC50 values and the various experimental conditions tested, except Mexel 432 concentration, were low. The mean LC50 values were 1.13+/-0.35 mg/liter after 3 days of exposure and 0.88+/-0.36 mg/liter after 7 days. In five spawns, it was 0. 69+/-0.32 mg/liter after 9 days. The lowest and highest LC50 values were 0.34 and 1.58 mg/liter after 7 days of exposure. Sensitivity to Mexel 432 increased slightly from the egg to the newly hatched larva and the developed larva. No lethality was observed during a period of recuperation after 4 days of exposure. The toxicity of Mexel 432 was not strongly reduced after 15 days of conservation of the solution. Vessel walls pretreated with Mexel 432 revealed no toxicity by contact or after eventual desorption. Methodological endpoints such as criteria for spawn quality, experimental conditions for the tests, demonstration of cumulative effects, and toxicometric importance of the period of mortality by starvation in fish early life toxicity tests are discussed.