The different modes of progression of renal diseases were studied in 73 patients by plotting the reciprocals (1/SCr) and logarithms (logSCr) of their serum creatinine values against time. The regression was linear in the reciprocal plot for 42 patients (57.5%) and in the logarithmic plot for 12 patients (16.4%). The type of renal disease did not predict the mode of progression. The deviations from the linear regression lines were probably most often due to changes in the level of blood pressure and to intensification of treatment for hypertension. The reciprocal plot turned out to be useful for predicting the date when end-stage renal failure was reached. An accuracy of 4 months was reached in 81.5% using the reciprocal plot but only in 25.9% using the logarithmic plot.