The immunological consequences of exposure to filarial infection were examined by cross-sectional serological studies. Serum samples from 121 pediatric patients (18 months-15 years of age) were analyzed in parallel with a panel of sera from adults residing in the same area of Haiti. Parasite antigen specific IgG and IgE levels were determined by ELISA. IgG levels in children were significantly elevated in humoral immunoreactivity to Brugia pahangi extracts compared to adults. In addition, anti-filarial IgG levels in amicrofilaremic children were significantly greater than in microfilaremic children. In contrast, IgG levels in adults were equivalent independent of microfilaremic status. Anti-filarial IgE levels in sera from both children and adults were low in comparison to that of a subject with tropical pulmonary eosinophilia and were unrelated to clinical status. No correlations were found between humoral responses and age, sex, or degree of parasitemia. Sera from amicrofilaremic children and, to a lesser extent, adults recognize more antigens, particularly those of high molecular weight (>55 kDa), than sera from microfilaremic patients.