Total post-heparin lipolytic activity (PHLA), hepatic triglyceride lipase (HTGL) and protamine inactivated lipoprotein lipase (LPL) and plasma lipoprotein pattern were investigated in 8 patients with acute renal failure (ARF). PHLA was determined at 5, 10, 15, 30, 45 and 60 minutes after heparin administration (100 U/kg b.w.). Maximal PHLA in ARF was 6.12 +/- 1.56 mumol FFA/ml/h at 10 minutes versus 14.62 +/- 4.29 at 45 min in controls (= 42%, p less than 0.001). PHLA was reduced in ARF throughout the study period (p less than 0.001). Maximal HTGL activity (3.06 +/- 0.84 mumol FFA/ml/h) was obtained at 10 min in ARF versus 8.97 +/- 3.11 after 15 min in controls (= 34%, p less than 0.001). HTGL in ARF differed from controls at all points of determination (p less than 0.001). LPL maximum was 3.12 +/- 1.93 mumol FFA/ml/h at 15 min in ARF and 7.65 +/- 3.44 at 45 min in controls (= 40%, p less than 0.001). LPL activity was different from controls at 30, 45 and 60 min (p less than 0.001) but not at 5, 10 and 15 min after heparin injection. Due to a rapid decrease of LPL activity (half maximal activity after 34 min in ARF versus 94 min in controls, p less than 0.05) activity half life of PHLA was diminished in ARF (49 min in ARF versus 112 min in controls, p less than 0.01). Thus both the activity of HTGL and LPL is impaired in ARF. Because of the different activation kinetics of the two PHLA fractions no conclusions concerning maximal enzyme activities can be drawn from single determinations as suggested in previous studies on chronic renal failure.