One method for assessing a child’s in utero exposure to environmental chemical pollutants is to measure the levels of biomarkers for these substances in biological samples collected at birth from the mother or the child. Conducted for surveillance purposes as part of the perinatal component of the national biomonitoring program, this approach is implemented within the biological component of the Elfe study. In October 2007, a pilot study involving 296 women was conducted to test the feasibility of the biological component of the Elfe cohort, whose nationwide enrollment took place in 2011. This report presents the results of biomarker assays performed on maternal urine collected at birth (cotinine, bisphenol A, phthalates, organotins, and certain pesticides) and mature breast milk collected one month after birth (dioxins, furans, PCBs, brominated flame retardants, and perfluorinated compounds). This pilot study provided initial findings on the exposure of pregnant women to environmental pollutants in France in 2007. These results were used to prioritize the biomarkers to be measured in the biomonitoring component of the national study. Furthermore, they led to the implementation, for this national phase, of precautionary measures aimed at preventing some of the potential contamination of biological samples by external sources at the time of sample collection. (R.A.)