There has been reported a decline in renal function with age, a decline that seems to accelerate after the age of 50. A systemically chosen sample of 70- and 75-year-old probands from the study '70-year-olds in Göteborg' have previously been examined with respect to GFR. The present study is a longitudinal follow-up of GFR in the previously examined 75-year-old probands at age 79. Renal tubular water absorption was also determined. In order to make a longitudinal comparison, S-creatinine was determined in a subsample of 166 probands, who had attended the study at 70, 75 and 79 years of age, by using frozen sera from these three examinations. S-creatinine increased slightly but statistically significant in both sexes between 70 years and 79 years of age. The reference values for EDTA clearance at age 79 calculated as M +/- 2 SD were 46-94 ml/min X 1.73 m2 BSA without any difference between the sexes. There was no change in GFR between 75 years and 79 years of age. We did not find any correlation between EDTA clearance and creatinine clearance. The tubular water reabsorption for probands without disorders was 843 +/- 92.6 (range 709-982). The results suggest that the renal filtration rate at age 79 is still good and that the ageing of the tubular function is not as pronounced as that of the GFR.