The bactericide triclosan is commonly used in e.g. plastics, textiles and health care products. In vitro studies on rat and human biological systems indicate that triclosan might exert adverse effects in humans. Triclosan has previously been found in human plasma and milk, but neither the primary source of human exposure nor the efficiency of triclosan transfer to human milk is known. In this study, plasma and milk were sampled from 36 mothers and analyzed for triclosan. Scrutinization of the women's personal care products revealed that nine of the mothers used toothpaste, deodorant or soap containing triclosan. Triclosan and/or its metabolites were omnipresent in the analyzed plasma and milk. The concentrations were higher in both plasma and milk from the mothers who used personal care products containing triclosan than in the mothers who did not. This demonstrated that personal care products containing triclosan were the dominant, but not the only, source of systemic exposure to triclosan. The concentrations were significantly higher in plasma than in milk, indicating that infant exposure to triclosan via breast milk is much less than the dose in the mother.