Warfarin requirements are lower in the Chinese, but it is not known if this applies to heparin. We investigated the optimal dose for heparin therapy in Chinese patients, and to assess relationship between i.v. heparin dosage and anticoagulation efficacy. One hundred Chinese patients requiring intravenous heparin therapy were given an initial bolus followed by continuous intravenous infusion. The main outcome measures were: (i) Efficacy of anticoagulation assessed by blood coagulation studies (APTT) compared to heparin dosage, (ii) Determinants of dosage variation-age, gender, body weight, height, indication for heparin therapy and number of medications, other disease, and serum albumin level. It was found that the mean therapeutic infusion dose requirement of heparin was 848.7 +/- 274.7 units/h, 79% required a dose of 1000 units/h or less. Heparin dose correlated negatively with age (r = -0.40; p < 0.001) and positively with weight (r = 0.44 p < 0.001) and height (r = 0.49; p < 0.001). Chinese subjects require lower heparin doses (about 800 units/h) than usually recommended for Caucasians (usual dose 1000-1500 units/h). This can be partly explained by the lower body weight in Chinese patients.