Rainbow trout eggs, yolk sac fry and juveniles were exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in different concentrations for 96 h. Exposure of eggs to the lowest concentration, used in this study, 0.1 ppt (10-13 glg), resulted in a significant growth retardation for 72 days. At higher concentrations significant numbers of the forthcoming fry developed generalized edemas and died. Histologically, degeneration and necrosis of liver parenchymal cells were observed. Remaining fry showed teratologic changes as foreshortened maxillas and opercular defects. Administration of TCDD to yolk sac fry had similar effects. Juvenile rainbow trout, exposed to 10 and 100 ppt TCCD for 96 h, showed growth retardation and developed slight edematous changes. At 100 ppt all fry had died within 27 days. Histologically, vacuolization of the liver parenchymal cells and intracellular inclusion bodies in liver, pancreas and stomach were observed.