Intestinal-type alkaline phosphatase (IAP) has been localized to the S3 segment of the renal tubule in previous studies, a site believed to be particularly vulnerable to toxic and ischaemic damage. During a 17-month period a pilot study of the value of urinary enzyme measurements (IAP and tissue non-specific alkaline phosphatase--TNAP, using monoclonal antibody-based immunoassays, and N-acetyl-beta-glucosaminidase--NAG, using colorimetric assay) in 50 prospectively followed cases of acute renal failure (ARF) was performed. Urinary enzymes were measured at initial evaluation ('start'), and then each day for 14 days, with the highest enzyme value ('peak') also used for analysis. Patients were divided into prerenal (n = 16), renal (n = 28), postrenal (n = 6) categories according to standard criteria. Of the renal ARF patients 23 of 28 had acute tubular necrosis (ATN), 3 of 28 acute interstitial nephritis (AIN), and 2 of 28 acute glomerulonephritis (AGN); 18 of 50 had a fatal outcome and 1 of 50 was dialysis-dependent at discharge ('poor' prognosis group), while 31 of 50 survived hospital without becoming dialysis-dependent ('good' prognosis group). Median enzyme concentration were increased in 'poor' compared to 'good' prognosis patients: start IAP 3.2 versus 2.2 U/g creat (NS), start NAG 48.6 versus 13.7 (P < 0.01), start TNAP 3.5 versus 0.9 (P < 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)