An effect of high blood pressure on the progression of renal functional deterioration was studied in 23 cases of chronic glomerulonephritis, which showed progressive renal functional impairments during the long-term follow-up period. The slope-of-regression line, which was obtained from the relation between reciprocal serum creatinine concentration (1/Cr) and observation time, was expressed as a progression rate and was evaluated on an association with blood pressure level. The progression rate was found to correlate significantly with the level of diastolic blood pressure (p less than 0.001). It is concluded that the elevation of blood pressure is one of the factors that contribute to the progression of renal functional impairment in chronic glomerulonephritis.