T-lymphocyte subpopulations bearing Fc receptors for IgM (T mu) or for IgG (T gamma) were studied in blood specimens obtained from 40 normal volunteers and from 16 patients with multiple myeloma. The myeloma patients showed a significant imbalance in T-cell subpopulations characterized by an increase in the percentages of T gamma cells to 30.0 +/- 3.9% (mean +/- SEM) compared with 12.0 +/- 3.0% for the controls (P less than 0.001). The patients exhibited a decreased proportion of T mu cells (13.4 +/- 4.1%) compared with the control value of 55 +/- 7% (P less than 0.001). When the results were analysed according to clinical status it was the patients with indolent or well-controlled disease and not those with progressive disease who exhibited an elevated proportion of T gamma cells. The elevation of T gamma cells or of a subpopulation of suppressor cells should be further studied as a possible mechanism of disease control in multiple myeloma.