Cell-mediated and humoral immune responses were assessed in 50 patients with type II or non-insulin-dependent diabetes mellitus and 50 nondiabetic patients with periodontitis. The values were compared with those of 50 age and sex-matched control subjects. The cell-mediated immunity assessed by enumerating the total and high-affinity rosette-forming cells of the patient did not show any significant variation from that of the normal control subjects. The humoral immune response was assessed by estimating serum immunoglobulins G, A, M, D, and E by single radial immunodiffusion. Except IgD, all other immunoglobulins were found to be elevated significantly in both diabetic and nondiabetic subjects. The alteration in humoral immune response may be the cause or the effect of periodontitis. The defective host response reported in diabetic patients may be responsible for the increased incidence of periodontitis in diabetic patients as compared to nondiabetic patients.