This report summarizes the deliberations of an eight-member panel of scientists convened by Dow AgroSciences in cooperation with the U.S. Environmental Protection Agency (EPA). The panel was charged with evaluating the scientific literature on the health effects potentially associated with exposure to the insecticide chlorpyrifos. Specifically, the panel was asked to (1) evaluate human experience data available and address the adequacy of the available current literature; (2) develop a list of recommendations for epidemiology studies, including appropriate endpoints and study populations, and strengths and weaknesses of each approach; and (3) draft a report to summarize its recommendations. The panel assessed the quality of the existing epidemiologic literature on chlorpyrifos and specific outcomes such as neuropathy (including organophosphate induced delayed neurotoxicity), behavior (cognition and affect), immunologic, and multiple complaints (also referred to as multiple chemical sensitivities). The majority of panel members (five members) agreed that the literature reviewed provided little or no scientific evidence that chlorpyrifos exposure causes harm to human health other than its known cholinergic effects associated with acute poisoning. Those panel members voting in the minority (three members) agreed that the studies reviewed provided inadequate evidence to preclude the possibility of adverse effects to human health from chlorpyrifos exposure at levels associated with its manufacture or professional application. Those voting in the minority suggested further investigation of cohort(s) of workers engaged in either the manufacture or the professional application of chlorpyrifos, or both. Compared to the general population, these groups have relatively high levels of exposure to chlorpyrifos. The primary health outcomes recommended for study were cognitive and affective disorders, with consideration of the assessment of peripheral neuropathy also suggested for at least a subset of the cohort.