Objectives-Risk factors for increased blood lead concentration (BPb) has been investigated. However, the eVect of sibship and Chinese herbal medicine on BPb has not been systematically studied. In this study BPb data from voluntary testing was used to determine if Chinese herbal medicine and sibship were associated with BPb. Methods-319 children aged 1-7 were tested for BPb. Meanwhile, parents were interviewed to obtain information including consumption of Chinese herbal medicine, living environment, lifestyle, and sibship of the children tested. Results-The mean (SD) BPb of 319 preschool children was 4.4 (2.4) µg/dl. The consumption of Ba-baw-san (a Chinese herbal medicine) was significantly associated with increased BPb in children (p=0.038). Further multivariate regression analysis of BPb in 50 pairs of siblings showed the factors of being brothers explained 75% of variation for BPb, and being sisters and brother-sister explained 51% and 41% of variation respectively. Conclusion-Chinese herbal medicine and children's play patterns within the family expressed in diVerent types of sibship are the main determinants of low concentrations of BPb in preschool children of Taiwan. (Occup Environ Med 1998;55:573-576)