Manganese (Mn) is an essential nutrient involved in many metabolic processes; however, epidemiological studies have shown associations between Mn neurobehavioral deficits and children, but these studies are unable to establish a causal relationship between Mn exposure and health effects. Therefore, in order to demonstrate causality, and to better understand the neurological effects of neonatal Mn exposure, it is best to use an animal model. Here, male rats were treated with Mn doses of 0, 25, and 50 mg/kg/day from postnatal day (PND) 1-21 or continuously exposed to Mn in doses of 0, 25, 50 mg/kg/day from PND 1-present. Animals were tested using an 8-arm radial maze (RAM) which evaluated spatial learning and memory functions. Based on previous findings using this maze paradigm (Kern et al 2010), we predict that neonatal Mn exposure will produce significant learning and memory deficits, and that prolonged exposure throughout life will produce even greater deficits, in a cumulative exposure – response relationship. On the other hand, if continuous Mn exposure is no more detrimental than pre-weaning exposure alone, one implication of this finding would be that the neonatal pre-weaning period is the development period of greatest susceptibility, perhaps due to the fragility of the brain during such a crucial time of development.