C3 and neoplasm: Immunological phenotyping of suspended cells showed that the tumour cells, irrespective of whether they were isolated from lymphoma tissue or from lymphoma tissue or from peripheral blood of leukaemic cases, bore a dense layer of surface immunoglobulin, lacked cytoplasmic immunoglobulin and receptors for mouse erythrocytes, and expressed both complement-receptor subtypes (i.e., receptors for C3b and C3d) in all but one case.