Lipase, in contrast to amylase, is completely reabsorbed by the proximal tubules after glomerular filtration. Therefore, no lipase is detectable in the unconcentrated urine according to the current opinion. The handling of lipase (detected with an enzyme-immunoassay) by the kidney was investigated in comparison with creatinine, amylase, and beta-2-microglobulin by clearance studies in acute pancreatitis (n = 10), burn injury (n = 4), glomerular proteinuria (n = 8), and controls without evidence of pancreatic or renal diseases (n = 5). In initial stages of acute pancreatitis a measurable clearance of lipase (mean: 49.6 microliters/min, range: 0.5-234) was found in association with corresponding increased clearances of beta-2-microglobulin (mean: 10.5 ml/min, range: 0.02-58.9) and of amylase (mean: 8.9 ml/min, range: 2.4-22.6) in nine of ten patients. This finding is consistent with a defect of tubular function. However, regression analysis failed to show a significant correlation between lipase and beta-2-microglobulin clearance. Repeated measurements during the course of pancreatitis in seven patients showed reversibility of tubular dysfunction. In patients with burn injury a similar elevation of clearances of beta-2-microglobulin and of amylase was found, but tubular dysfunction in this condition was not associated with lipasuria. In glomerular proteinuria a lipase clearance was found in two of five cases with moderate, and in the other three cases with severe impairment of creatinine clearance. beta-2-microglobulin clearance was normal in the former and only slightly elevated in the latter group. In conclusion lipase is measurable in the urine of most patients with acute pancreatitis as a result of a reversible tubular dysfunction.(ABSTRACT TRUNCATED AT 250 WORDS)