Five-month-old female Sherman rats were dosed by gavage with 0 or 500 mg of Firemaster BP-6 (polybrominated biphenyls, PBBs) per kg body weight as a 5% solution in corn oil and then maintained on normal diet and waterad libitum. Urine pools from test and control groups of five fasting rats were collected once a month, up to 179 days after the test rats were dosed. PBB-dosed animals showed significantly higher (p=0.0003) creatinine-corrected proteinuria. Two-dimensional electrophoresis (2DE) and silver staining were used to determine differences in urinary protein patterns between test and control rats. Dosed animals excreted new proteins with higher molecular weight and more basic isoelectric points than controls. The appearance of numerous, new proteins excreted by the PBB-dosed rats demonstrates the utility of 2DE for the sensitive detection of possible health effects from toxicant exposure.