A 30% burn injury has been previously reported to impair mitogenic response of splenocytes to a B-lymphocyte mitogen and to affect serum levels of serum class-specific immunoglobulin. To further investigate the effect of burn injury on the function of B lymphocytes in gut-associated and systemic immune tissues, we studied class-specific immunoglobulin synthesis by cultured lymphocytes from spleen and mesenteric lymph nodes after burn injury in rats. Male Lewis rats received 30% full-thickness burn injuries, and 4 days later, the animals were killed to remove spleen and mesenteric lymph nodes. The cells from spleen and mesenteric lymph nodes were cultured for 5 days with 25 micrograms/ml of lipopolysaccharide. Concentrations of immunoglobulin G (IgG), IgM, and IgA in the supernatant of each well were then measured with enzyme-linked immunosorbent assay for class-specific immunoglobulin. Synthesis of IgG by lymphocytes from spleen was statistically significantly impaired by burn injury (p less than 0.05), but synthesis of IgG by lymphocytes from mesenteric lymph nodes was not affected. There were no significant differences in IgM and IgA synthesis by lymphocytes from spleen between burned animals and controls. The immunoglobulin synthesis in mesenteric lymph nodes did not differ significantly in burned animals compared with controls. The impaired IgG synthesis by lymphocytes from spleen may contribute to increased risk of infection after burn injury.