Estrogen-receptor-like binding was partiallycharacterized in liver tissue of prespawning female largemouth bass,Micropterus salmoides (LMB). Saturation and Scatchard analysesexhibited estrogen binding activity with high affinity (Kd in the10(-9) M range) and limited capacity (nuclear = 37.4fmol/g tissue; cytosol = 234 fmol/g tissue). Androgens, progestins,and cortisol competed poorly for binding in competition studies. Thus, LMBliver estrogen binding activity possesses similar properties to estrogenreceptors (ER) described in other vertebrates.In a study of prespawning female LMB from Lake Hartwell, SC/GA, a reservoir contaminated bypolychlorinated biphenyls (PCBs), individuals environmentally exposed to highlevels of PCBs had significantly lower ER binding capacity (Bmax) and highernonspecific binding (NS) than fish from a relatively uncontaminated referencelocation. Fish obtained at a site with intermediate levels of PCBs did notexhibit the expected decrease in Bmax. The lower Bmax observed in fish fromthe location with high PCB contamination is consistent with the reportedbehavior of liver ER in fish experimentally exposed to PCBs. Increased NS inthe ER assays could be related to elevations in albumin associated with thePCB exposure.