Total IgE and IgG serum levels were measured in rats treated with egg albumin (EA), Bordetella pertussis (Bp) and aluminium hydroxide gel (alum), and in rats administered with Bordetella pertussis or alum alone. Two ELISA micromethods have been developed to measure IgE and IgG changes. Immunoglobulin serum levels were evaluated 14 days after immunization. The highest IgE levels were obtained after sensitization with EA suspended in alum s.c. and administered with Bp i.p. The IgE production induced by Bp alone was significantly lower than that of the former. The IgE concentrations from alum treated group were the same as those obtained in the untreated animals. IgG serum levels remained unchanged in the different immunization procedures assayed.