Effects of perinatal exposure to polychlorinated biphenyls (PCBs) on auditory P300 latencies and amplitudes were evaluated in children from a Rotterdam cohort. From this cohort of healthy, term babies, the 26 lowest and 26 highest prenatally PCB-exposed children from the breastfed and the formula-fed groups (n=104) were invited for P300 assessment when they were 9 years of age. For P300 assessment an auditory simple odd-ball paradigm was used. In the 83 participating children, 60 assessments (32 males, 28 females) satisfied the measurement criteria and were included in the data analyses. After adjusting for confounding variables, children with high prenatal exposure were found to have longer P300 latencies than children with low prenatal exposure. Lactational exposure to PCBs through breastfeeding milk was not related to P300 latencies. P300 latencies were shorter in children breast-fed for at least 16 weeks than in children breastfed for 6 to 16 weeks and formula-fed children. P300 amplitudes were not related to perinatal PCB exposure nor breastfeeding. Results of this exploratory study suggest that prenatal exposure to environmental levels of PCBs and related compounds delays mechanisms in the central nervous system that evaluate and process relevant stimuli, whereas breastfeeding accelerates these mechanisms.