T-cell subpopulations have been implicated in the regulation of normal human B-cell reactivity. As the non-Hodgkin lymphomas (NHL) represent predominantly clonal B-cell malignancies, we examined the relationship of total T-cell [Sheep Red Blood Cell (SRBC) binding] and Fc gamma bearing T-cell populations in these disorders. Peripheral blood from seven low-grade (Rai stage 0), six high-grade (Rai stage 3 or 4) CLL patients, lymph node specimens from five patients with WDLL, seven patients with PDLL-D, three patients with MC-D, and eight patients with DHL were studied. All values were compared to normal controls. The percentage of total T cells in each disease category was decreased compared to controls. In addition, there was a reproducible correlation between the percentage of Fc gamma bearing T cells and the histopathologic diagnosis. The percentage of Fc gamma bearing T cells was highest in low-grade CLL and decreased incremently from high-grade CLL and WDLL, to MC-D, and PDLL-D. In DHL, we found no Fc gamma bearing T cells. Finally, the percentage of Fc gamma bearing T cells in each disease category was decreased compared to controls. These findings suggest a correlation between Fc gamma bearing T cells and the clinical aggressiveness of disease in NHL. In addition, they may raise important questions about therapy. Finally, they may offer a useful clinical test as an adjunct to histopathology although this will need to be confirmed in larger series.