Fifty-three patients with osteomyelitis were grouped according to the duration of the disease at presentation, the bone and the part involved, the aetiology, activity, severity and stage of disease. Sera from these patients was estimated for IgA, IgM and IgG levels and in 23 matched controls. The results were compared with the normal range, and correlative studies were carried out between serum immunoglobulin levels and the different clinical parameters. Serum levels of the 3 immunoglobulins were found, in general, to fail to rise above the normal in the presence of infection. Furthermore, the levels did not show significant variation with the clinical parameters. These findings suggest that there is an intrinsically subdued immune response to osteomyelitis in most of the patients, partly confirming the suspicion of an immunodeficient state.