The purpose of the present study was to evaluate the effects of chronic exposure to chemical pollutants on cell mediated immune responses in a pediatric population living in Priolo, an industrialized area of Italy, by means of skin test (Multitest CMI). The results suggest that children living in Priolo display significantly lower delayed type hypersensitivity (DTH) response than those seen in an age-matched and socioeconomically similar group of children living in Taormina, a nonindustrialized area. The lowered incidence of DTH scores in Priolo is not due to the number of positive skin test responses to individual antigens, but rather to the size of individual reactions.