We report a case of diffuse large-cell lymphoma which pursued a clinically indolent course while remaining untreated. The tumor cells expressed surface IgG, CD10, CD19 and CD20, but not surface IgM, IgD, IgA, CD5, CD16, CD32 and CD64. In addition, these cells appeared to coexpress kappa- and lambda-light chains on their surface. JH and J lambda genes were monoclonally rearranged, but not the J kappa gene. The present lymphoma was found to have arisen from follicle center cells expressing IgG lambda, while the surface kappa-light chain seemed to be extrinsic. Furthermore, the extrinsic immunoglobulin bearing the kappa-light chain may have belonged to IgG because no surface immunoglobulins other than IgG were detected on the cell surface. Then, the extrinsic IgG may have combined with certain molecules on the tumor-cell surface through its Fab portion because the tumor cells lacked all three receptors for the IgG-Fe portion. Fc gamma RI (CD64). Fc gamma RII (CD32) and Fc gamma RIII (CD16). From these findings and the patient's history of never having received a blood transfusion, we concluded that the present case might be of a B-cell lymphoma possibly coated with an IgG-type autoantibody which appeared to have anti-idiotypic activity.