After determination of the lithogenic and inhibitory substances in serum and urine of 18 healthy control subjects and 20 patients with calcium oxalate urolithiasis on an uncontrolled diet, the alteration of the parameters while taking a standard diet was investigated. After attainment of a steady state, the investigations were performed over 48 h on 3-h aliquots of urine. Typical circadian rhythms were detected for all lithogenic parameters in the urine and normal ranges were established. This special investigation permits detection of "peaks" in the excretion of lithogenic substances which were masked in investigation of 24-h urine samples alone.