Reproductive parameters and accumulation of chlorophenolic compounds by white sucker (Catostomus commersoni) populations exposed to bleached kraft mill effluent (BKME) were studied in the St. Maurice River, Quebec. Compared with unexposed populations from the same waterway, exposed white sucker showed obvious effects of chemical exposure as far as 100 km downstream of the mill, as revealed by a strong induction of ethoxyresorufin O-deethylase (EROD) activity. In males, circulating plasma testosterone levels were the same at all sites, while 11 -ketotestosterone levels were significantly lower at exposed stations. In females, testosterone and 17β-estradiol levels were significantly reduced at the two exposed stations relative to the reference station. Despite different hormone levels during sexual maturation, gonad weight as a proportion of carcass weight was similar at all sites for both sexes during early gonadal development. The relationship between carcass weight and fecundity was more variable at the station immediately downstream of the mill. Biochemical and physiological parameters measured in this study do not allow us to clearly relate perturbations in plasma steroid levels to impaired reproduction as measured by gonad weight and fecundity.