Quantitative and functional abnormalities of T and B lymphocytes and monocytes have been described in Hodgkin's disease (HD) and non-Hodgkin's lymphomas (NHL), thus making both diseases suitable models to study the interactions between lymphoid and myeloid systems. We evaluated the growth of colony-forming units of granulocytes and monocytes/macrophages (CFU-GM), as well as the colony-stimulating activity (GM-CSA) produced by monocytes and the colony-inhibiting activity (GM-CIA) released by autologous rosette-forming T-cells (Tar cells), a postthymic precursor subpopulation, in peripheral blood samples from 7 patients with HD and 5 with NHL. CFU-GM growth in HD and NHL patients was similar to that observed in controls. However, GM-CSA and GM-CIA were significantly decreased in both HD (p = 0.002 and p = 0.012, respectively) and NHL (p = 0.003 and p = 0.017, respectively) patients as compared to controls. These data suggest that cytokine-dependent mechanisms regulating normal CFU-GM proliferation are impaired in HD and NHL.