The existence of circadian variations in the urinary excretion of total protein, albumin and creatinine was investigated in subjects with normal and impaired renal function. All individuals were kept at bedrest for 24 hours. Eight consecutive urine specimens were collected every 3 hours and examined. In normal subjects the urinary total protein, albumin and creatinine excretion showed a significant increase during the 12 daytime hours compared with the night-time. The diurnal variations with peak occurrence at 13.26 h (range 09.58-16.43 h) for total protein, at 12.37 h (range 10.33-15.18 h) for albumin, at 16.33 h (range 13.22-19.24 h) for creatinine are temporally related to the ingestion of meat. In patients, by contrast, total protein, albumin and creatinine excretion in the urine were not modified significantly throughout the 24 hours period. Thus, impaired renal function is associated with the loss of the physiological circadian rhythm.