Lymphocytes obtained from the blood of normal individuals and six patients with newly diagnosed multiple myeloma were separated into T and non-T cell populations by rosette-formation with sheep erythrocytes, and were then assayed for the presence of surface membrane Fc receptors. When compared with normal individuals, four patients with IgG myeloma had a three- to fourfold increase in T cells with IgG receptors (T gamma cells) and two patients with IgA myeloma had a two- to threefold increase in T cells with IgA receptors (T alpha cells). Patients with IgG or IgA myeloma had normal numbers of non-T lymphocytes with surface receptors for IgG and IgA, respectively. The finding that human myeloma is accompanied by elevated numbers of T cells with Fc receptors for the heavy chain class of the myeloma protein: (1) may account for the apparent "monoclonal" lymphocyte population in patients with myeloma; (b) extends to humans similar observations made in mice with secretory plasmacytomas; and (c) is of interest because T cells with Fc receptors are immunoregulatory lymphocytes.