Nine of twelve consecutive patients with a solitary functioning kidney treated for renal stone by extracorporeal shock wave lithotripsy (SWL) with the modified Dornier HM3 lithotripter were evaluated before and 20 months (range 12-24 months) after treatment by detailed renal cortical and tubular function tests. Urinary excretion of the renal tubular enzymes N-acetyl-beta-glucosaminidase (NAG), alkaline phosphatase (ALP), and kallikrein and of albumin and beta-2-microglobulin was unchanged. Clearances of creatinine (C(Cr)), inulin (C(IN)) and para-aminohippuric acid (C(PAH)) and filtration fraction (FF) were constant, as were serum levels of creatinine, urea, and beta-2-microglobulin. In seven of the nine patients, however, C(IN) was decreased at follow-up by a mean of 15% (range 5% to 54%), and C(PAH) was decreased by a mean of 30% (range 3% to 58%) in six of the nine patients. Plasma renin activity (PRA) and serum aldosterone were stable, and no patient developed new-onset hypertension.