The present study was undertaken to investigate whether the development of proteinuria in the borderline hypertensive rat (BHR) is influenced by the Y chromosome and to determine if the onset of proteinuria in the BHR is delayed when blood pressure is lowered with enalapril, an angiotensin I converting enzyme inhibitor. Male Fι, rats were the first-generation offspring of the mating of spontaneously hypertensive (SHR) females and Wistar-Kyoto (WKY) males and the mating of SHR males and WKY females. At 20 weeks of age, enalapril (125 mg/l) was added to the drinking water. Untreated BHR and enalapril-treated BHR (BHRE) were followed to 90-100 weeks of age. Urine was collected every 10-20 weeks for determination of protein, albumin, and nitric oxide (NO2/NO3) metabolite excretion. Indirect blood pressure in BHR from both crosses was approximately 175 mm Hg from 20 to 90-100 weeks of age. Enalapril lowered blood pressure by about 30 mm Hg, but was ineffective in reducing urinary protein or albumin excretion rates at any age. Urinary excretion of nitric oxide metabolites was similar in all groups at all time periods. There were significant differences in the percent of glomerulosclerosis between the two matings. Based on these results, renal injury in the BHR is not associated with the Y chromosome and can be dissociated from hypertension. Further studies using congenic and transgenic technology will be necessary to identify functions of genes and associations with hypertension in order to understand the kidney disease in this model of hypertension.