The relationship between blood lead (7439921) levels and maximal motor nerve conduction velocity was assessed using data from an earlier study of childhood lead exposure. The original study related blood lead levels to airborne lead in a population of children between the ages of five and nine years who lived near a primary lead smelter in Kellogg, Idaho. A total of 202 asymptomatic children were identified who had blood lead levels greater than 40 micrograms per decaliter (microg/dl). A total of 123 asymptomatic high lead children were pair matched with children residing in the same area and of the same gender and socioeconomic class but who had blood lead levels less than 40microg/dl. A second control population consisted of 53 five to nine year old children residing in an uncontaminated rural area of northern Idaho. The children were evaluated by standard medical and neurological procedures, and the maximal motor nerve conduction velocity was measured in the right peroneal nerve using cutaneous electrodes. Backward stepwise regression analyses of the data correlated the blood lead data with area and duration of residence, age, sex, Hollingshead index of socioeconomic status, pica, and free erythrocyte protoporphyrin. The area of residence, age, and history of pica were significantly related to blood lead level, and the blood lead level was the only variable determined to be significantly related to the nerve conduction velocity. A threshold effect between blood lead level and nerve conduction velocity was established at blood lead levels of between 20 and 30microg/dl using hockey stick, logistic, and quadratic regression analyses.