Methods Forty-four patients with the adult form of polycystic renal disease were examined. The diagnosis was made by abdominal palpation, intravenous urography, sonography and/or computerized axial tomography. Twenty-nine patients were seen on several occasions; the mean follow-up was 8.4 4.5 (SE) years (range, 2 to 21 years). At the first examination it was discovered that the youngest patient was 21 and the oldest was 75. Seventeen patients reached the stage of terminal renal failure during the follow-up period. At that time their mean age was 47.8 10.3 (SE) years (range, 27 to 68 years). Fifty-six single or serial 5tCr-EDTA (or inulin) and PAH clearance determinations were performed in 38 patients; in 21 of them repeated measurements of serum creatinine were also available. In an additional group of six subjects, serial serum creatinine values only were used as an index of renal function. The total number of serum creatinine determinations in these 27 patients was 111. The rate of deterioration was followed by comparing the reciprocal creatinine values. In all subjects blood pressure was measured frequently by the cuff method, and urine cultures were performed repeatedly. The diagnosis of urinary infection was based on positive urine cultures, leucocy-tuna and at least one of the following symptoms: dysuria, lumbar pain, fever, and elevated blood sedimentation rate (BSR). The glomerular filtration rate (GFR) was measured by the 51Cr-EDTA clearance (in some patients the inulin clearance), and the effective renal plasma flow was estimated by the PAH-clearance (CPAH). The conventional procedure was applied to the patients in a supine position with a constant infusion of the indicators and an indwelling catheter in the urinary bladder [2—41. Serum creatinine was determined with an autoanalyzer (Greiner-Analyzer II)[51.