In order to investigate whether or not primary glomerulonephritic patients have abnormal diurnal water, sodium, and potassium excretion and its relation to diurnal urinary kallikrein excretion (UKE)., we studied the diurnal patterns of urinary water, sodium, potassium, and kallikrein excretion in 16 primary glomerulonephritic patients and 12 normal persons. Urinary kallikrein activity was measured by the enzymatic hydrolysis of synthetic chromogenic substrate S-2266, and urinary electrolytes were measured by flame photometry. The day, night, and 24-hour urine outputs were significantly higher in glomerulonephritic patients, but urinary sodium, potassium and kallikrein excretion at all periods of collection did not differ between glomerulonephritic patients and normal controls. UKE was positively correlated with urinary potassium excretion in both normal controls (r = 0.5, p less than 0.05) and glomerulonephritic patients (r = 0.66, p less than 0.01), whereas no correlation existed between UKE and urinary water excretion, or UKE and urinary sodium excretion in either group. The day/night output ratio of water, sodium and potassium excretion were not different between glomerulonephritic patients and normal subjects. These results indicate that: (1) there is no abnormal diurnal water, sodium, potassium, and kallikrein excretion in primary glomerulonephritic patients with fair renal function; and (2) urinary kallikrein may play a role in the regulation of urinary potassium excretion.