Toxicity test protocols were developed for larvae of two species of marine fishes of the Pacific coast of the United States. During winter months, larvae were obtained from adult English sole (Parophrys vetulus) spawned in the laboratory. Newly-hatched, nonfeeding larvae were used in 96-hr experiments to determine their acute sensitivity to inorganic and organic toxicants. Exposure to ZnSO(4) produced a 96-hr LC(50) of 14.5 mg Zn/L. A complex and variable organic effluent (untreated bleached kraft mill effluent; BKME) yielded 96-hr LC(50)s ranging from 1.2-9.3% BKME.Larvae were obtained from eggs collected from wild and laboratory populations of the spring and summer-spawning topsmelt (Atherinops affinis). Both acute (96-hr) mortality and longer-term (7-14 days) growth responses of topsmelt larvae to BKME were determined. Acute toxicity levels (96-hr LC(50)s) ranged from 6.2-9.7% BKME. No Observed Effect Levels (NOELs) for 7 and 14 day exposures ranged from 1.0-3.0% BKME.