The cytokine and antibody response to Trichuris trichiura infection was determined for 96 persons living in an area where the parasite is highly endemic and infection exhibits a convex age intensity profile. In response to stimulation with T. trichiura antigen, a small proportion of the study group produced interleukin (IL)-4 (7%), IL-9 (5%), and IL-13 (17%). A larger proportion produced IL-10 (97%), tumor necrosis factor (TNF)-alpha (93%), and interferon (IFN)-gamma (32%). The levels of TNF-alpha (P =.016) and IFN-gamma (P =.012) significantly increased with age, suggesting a switch to a more chronic infection phenotype. The predominant parasite-specific antibodies produced were IgG1, IgG4, IgA, and IgE. Unlike the IgG subclasses and IgA, parasite-specific IgE correlated negatively with infection intensity, as defined by egg output (P =.008), and positively with host age (P =.010). These findings suggest a mixed cytokine response in trichuriasis and an IgE-associated level of protection.