The objective of the study was to demonstrate the bioequivalence of subcutaneously (s.c.) and intravenously (i.v.) administered fixed, high-dose low-molecular-weight heparin (LMWH) on anti-activated factor X activity (anti-FXa). Secondary objectives were the analysis of the pharmacodynamic effects on Heptest, thrombin inhibition, tissue factor pathway inhibitor (TFPI), and the urinary excretion of LMWH in the randomized cross-over study following i.v. and s.c. application of 8000 anti-FXa units LMWH Certoparin in 18 healthy subjects. The bioequivalence following s.c. administration was demonstrated from the antilog of the point estimator for the application differences (s.c. minus i.v.) by an area under the activity-time curve (0-24 h) of 101% (range, 93-110%). LMWH was bioequivalent also on Heptest and TFPI, and was 50% on thrombin inhibition. The urinary excretion of biologically active material was 4.1 and 3.6% following i.v. and s.c. administration, respectively. Differences in the pharmacodynamic parameters of the assays indicate specific biological actions of high and low molecular sacharide chains of the LMWH.