Sodium fluoride was administered at 0, 25, 50, 100, and 150 ppm F in drinking water for 4 weeks to Institute of Cancer Research (ICR) derived glomerulonephritis (ICGN) mice. Fluoride was also administered to ICR mice at 0 and 150 ppm. Blood was sampled from the tail artery of each mouse twice a week for the determination of blood urea nitrogen (BUN) and creatinine (CRE). All ICGN mice in the 150 ppm F group and 4 of 9 in the 100 ppm F group died before the end of four weeks, but no ICR control mice died. The mean values of BUN and CRE in the serum of the 150 ppm ICGN mice were significantly higher than those in the ICGN control mice at the end of the exposure period. The mean relative liver weight of the 150 ppm ICGN mice was significantly lower than that of the ICGN control mice. We conclude that F significantly exacerbates renal dysfunction.