Renal function was assessed in prestroke and poststroke Kyoto-Wistar stroke-prone spontaneously hypertensive rats (SHRsp) fed high-K+ (2.11%) and low-K+ (0.75%) diets containing 4% NaCl and in stroke-resistant SHR (srSHR) fed a low-K+ diet. Elevations in dietary K+ retarded the onset of stroke development in SHRsp, but did not alter the life-span of SHRsp between the onset of stroke and death. At ages 12 weeks, hemorrhagic stroke rapidly developed in SHRsp. When compared with srSHR, prestroke SHRsp exhibited higher serum creatinine and urea levels, a greater excretion of protein into the urine, and lower serum albumin levels. The severity of the above indices of renal failure was amplified in similar-aged poststroke SHRsp. Poststroke SHRsp also had elevated levels of hemoglobin in the urine. Increases in dietary K+ did not significantly decrease the severity of uremia and proteinuria in age-matched prestroke or poststroke SHRsp. It was concluded that a decrease in glomerular filtration, uremia, and proteinuria preceded stroke development in SHRsp. The onset of proteinuria and uremia in SHRsp could potentiate stroke development. The latter indices of renal function were not altered by modifications in dietary K+ that retard stroke development in SHRsp.