The immune status of trauma patients was compared with that of elective surgery patients and normal controls. The trauma patients, the elective surgery patients, and the controls were all male, aged 18 to 36 years, in previous good health and with similar Injury Severity Scores. Only one of eight immunologic activities assayed distinguished between these groups of subjects. It was observed that the synthesis and secretion of immunoglobulins (Ig) in vitro by the circulating B cells of the trauma patients was markedly impaired when compared to Ig synthesis by B cells of the elective surgery patients or controls. Furthermore, it was demonstrated that the B cells, and not the T cells, Null cells, or monocytes, were defective in the trauma patients. The results indicate that diminished Ig synthesis and secretion by the circulating B cells of the trauma patients cannot be attributed to the surgery; rather, it appears that the defects in the B cells are a direct result of the trauma.