The relative risks (odds ratio, OR) of various risk factors for venous thrombophilia, including sex, antithrombin III, protein C (PC), protein S (PS) and plasminogen deficiencies, and C677T homozygous mutation of methylenetetrahydrofolate reductase gene were assessed using age matched (+/- 5 years) conditional logistic regression analysis in 116 Chinese venous thrombophilic patients (58 males; 58 females, mean age 47.5 +/- 17.7 [SD] years) and 125 healthy controls (67 males; 58 females, mean age 45.5 +/- 15.7 years). None of the patients had prothrombin G20210A and factor V Leiden mutation or an activated PC sensitivity ratio of less than 2, One hundred and five age-matched patients and 105 controls were entered in this analysis. Only PC and PS deficiencies were significantly associated with increased risk for the development of thrombosis with an OR of 10.6 (95% confidence interval 2.3-49.9, P = 0.0028) and 6.7 (2.7-16.5, P = 0.0001), respectively. The findings of this study suggest that PC deficiency and PS deficiency are the most important risk factors for thrombosis in Chinese venous thrombophilic patients. (C) 2000 Elsevier Science Ltd, All rights reserved.