The effect of blood pressure on progression of renal insufficiency was examined in a large group of patients who eventually required dialysis. Out of 198 consecutive new chronic dialysis patients, 86 had sufficient data predialysis to determine rates of progression of renal insufficiency by reciprocal creatinine versus time plots. Average plasma creatinine at first contact was 3.8 +/- 0.2 mg/dl and at the time of dialysis was 11.4 +/- 0.4 mg/dl. Mean duration of follow-up was 33.4 +/- 2.5 months and the average rate of decline in reciprocal creatinine was -0.009 +/- 0.001 dl/mg month. Patients were stratified by average value of diastolic blood pressure measured in clinic. Patients in the lowest quartile had a rate of decline in reciprocal creatinine of -0.007 +/- 0.001 dl/mg month, which was slower than that of patients in the third and fourth quartiles, -0.010 +/- 0.001 and -0.011 +/- -0.002 dl/mg month, respectively (P less than 0.05). In individual patients, a mean diastolic BP of less than 90 mm Hg was associated with a rate of decline in reciprocal creatinine of -0.006 +/- 0.001 dl/mg month which was significantly less than the rate of -0.009 +/- 0.001 when the diastolic BP was greater than 90 mm Hg. Thus, in a large group of patients who have progressed to ESRD, there is an association between control of diastolic blood pressure and a slower rate of decline in renal function.