Wild white sucker exposed to bleach kraft mill effluent (BKME) from two mills using chlorine bleaching were analyzed for concentrations of extractable organochlorines (EOCl\sbL μg Cl/g lipid) in different tissues. The factors site (reference vs. BKME-exposed), sex (male vs female) and tissue (carcass, whole fish, liver, muscle, gonad and intestinal fat) were examined for their effect on EOCl\sbL concentrations. White sucker EOCl\sbL concentrations were also compared during a change from 100% molecular chlorine bleaching to 70% chlorine dioxide substitution to assess whether implementation of modern bleaching technology would result in a decrease in the amount of organochlorines accumulated. Only 1-15% of the EOCl in fish can be attributed to known substances. It has been suggested that the EOCl in fish exposed to BKME is composed of chlorinated lipid (Wesen, 1995). To investigate this, gel permeation chromatography (GPC) was used to purify the lipid in EOCl extracts, and this lipid was subjected to several chemical fractionation techniques to determine where the chlorine was bound in the lipid.