The lymphocyte marker pattern of non-Hodgkin's lymphoma cells was related to current concepts of lymphoma classification. In a series of 28 lymphomas lymphocyte markers indicated that 2 were of histiocytic origin, 2 were unclassifiable, none were derived from T cells and the remainder were B-cell neoplasms. The immunoglobulin heavy chain associated with the B-cell tumours was gamma in one case, alpha in one case but was mu in the majority of cases, reflecting the predominance of this heavy chain, together with delta chains, on normal lymph node lymphocytes in man. delta chains accompanied mu chains on the tumour cells in 6/17 lymphomas in which anti-delta staining was performed. delta chains were not found on any lymphomas other than well differentiated diffuse lymphocytic types. There was evidence of a reduction in surface immunoglobulin, Fcgamma and C3 receptors on undifferentiated lymphoma cells. T lymphocytes of normal morphology were present in all lymphomas except one, and were more numerous in follicular lymphomas than in diffuse tumours.