The latent and hypertonic forms of the course of compensated nephritides more frequently make difficulties concerning the differential diagnosis between a chronic glomerulonephritis and a chronic pyelonephritis. According to the results achieved the determination of the renal processes furthering homoeostasis gives the possibility to demarcate the two diseases. A certain reduction of the creatinine clearance (to less than 90 ml/min) and of the maximum water diuresis (to less than 10.0 per 100 ml glomerular filtrate) is suitable for the latent form of the chronic glomerulonephritis. On the other hand, a reduction of the ammonia secretion (to less than 35 per 100 ml glomerular (filtrate) and of the total H+-ion secretion (to less than 50 per 100 ml glomerular filtrate) in the determination after Alkinton is characteristic for the chronic pyelonephritis. In the hypertensive form of the course of the chronic glomerulonephritis in contrast to the same form in chronic pyelonephritis a reduction of the maximum water diuresis to less than 7.5, of the clearance of the "osmotically free" water to less than 6.0, of the titrable acidity to less than 25 is the result. Here the ammonia quotient transgresses 45%. In chronic pyelonephritis the titrable acidity in considerably increased and the ammonia genesis relatively decreased (to less than 45%).