A radioimmunoassay for quantitation of the human pancreatic estrogen binding protein (hEBP) was developed using polyclonal rabbit hEBP antiserum and iodinated purified hEBP. Parallel dose-response curves were obtained when serial dilutions of human serum and of cytosols obtained from human pancreas, prostate and colon were analyzed simultaneously with serial dilutions of purified hEBP standard. Very high levels of hEBP (500-1000 mg/kg wet weight) were found in normal pancreas. High as well as medium levels were found in pancreatic carcinoma tissue and medium values (0.1-1 mg/kg wet weight) in prostate, colon and ovarian tissue. Other tissues and serum from healthy volunteers showed low values, usually below 0.1 mg/kg. When serial dilutions of rat pancreatic cytosol were analyzed in the hEBP assay, [125I]hEBP was displaced by the rat preparation, but the dose-response curves were not parallel to the standard curves, indicating similarity but non-identity between the estrogen binding proteins in human and in rat pancreas.