An in vitro culture technique with synthesis of 14C-labeled protein has been used to study immunoglobulin and specific-antibody formation by spleen, mesenteric lymph nodes, Peyer's patches, and small intestine of rabbits, which were immunized twice subcutaneously with Vibrio cholerae lipopolysaccharide (LPS) and enterotoxin; saline-injected rabbits served as controls. Newly synthesized immunoglobulin G (IgG), IgA, and IgM were quantitated by liquid scintillation after their isolation by means of affinity chromatography from columns with immunoglobulin class-specific antibodies coupled to Sepharose. Specific antibodies were similarly measured after purification from gels derivatized with LPS or cholera toxin. The isolated antibodies had full biological activity as studied in protection tests. The immunization increased the overall IgM synthesis in the spleen. It also enhanced the production of IgA and IgG in Peyer's patches and of IgA in intestine. Significant synthesis of radiolabeled antibodies against both V. cholerae LPS and enterotoxin was found in spleen as well as in Peyer's patches of immunized animals. Titration with an enzyme-linked immunosorbent assay (ELISA) showed significant levels of IgG as well as IgA antibodies in incubation medium from all the studied tissues, whereas specific IgM was only found for spleen and mesenteric lymph nodes. Simultaneous tissue incubations at 37 degrees C and in an ice bath indicated that the major part of the antibodies registered with the ELISA represented de novo synthesis.