The main purpose of this research is to examine the consequences of in utero exposure to PCBs on Inuit infants, from birth to 11 months of age. Of particular interest is the impact of PCBs and mercury exposure on newborn’s thyroid hormones, physical growth, physical and central nervous system maturity, on infant’s overall health, mental, psychomotor and neurobehavioral development, and on functional and neural impairment in the domains of visual and spatial information processing. The proposed project is designed to replicate and extend previous findings by studying a more highly exposed cohort of infant, and using new infant assessment paradigms that have been linked to specific brain regions and neural pathways and, therefore, have a potential to provide information regarding possible mechanisms of action. The second objective of this research is to document the exposure to heavy metals, organochlorines and polyunsaturated fatty acids of newborns from selected communities in Nunavik. This ongoing effect study provides the opportunity to perform long time trend analysis of human exposure (data available for same communities since 1993).