The pharmacokinetic and pharmacodynamic characteristics of heparin were studied in 10 healthy volunteers using the Hepcon/System B-10. This coagulation-monitoring system uses each patient's body weight, height, baseline activated clotting time (ACT), and heparin dose response values to determine initial heparin doses. We administered a calculated mean +/- SD heparin doses of 85 +/- 14 U/kg to 10 subjects to achieve a mean +/- SD target ACT of 364 +/- 29 seconds. This dose produced a mean +/- SD measured peak ACT of 337 +/- 53 seconds from a mean +/- SD baseline of 121 +/- 10 seconds. The measured peak ACT values resulting from the individualized heparin doses were within 20% of the desired peak in 9 (90%) of the subjects. Using the ACT values, the average mean residence time for heparin effect was 1.2 hours and half-life was 0.8 +/- 0.2 hours, with all the subjects' values returning to within 10% of baseline by 4 hours after the dose. Using the protamine-derived heparin concentrations, heparin total-body clearance ranged from 43 to 99 ml/hr/kg (mean +/- SD 73.3 +/- 14.5 ml/hr/kg). A linear relationship was found between heparin concentration and change in ACT that was described by delta ACT = 16.85 + 136.7.(heparin concentration). We conclude that this method is easy to perform and accurate for determining initial heparin dosage requirements, and could be an important improvement over existing approaches. In addition, it is a valuable research tool for studying heparin pharmacodynamics and pharmacokinetics.