Cytokines are regulatory molecules that are produced by a variety of cell types and are characterized by numerous biologic functions involved in the regulation of the immune system and hematopoiesis. This review summarizes the functions and regulation of cytokines in lymphomas and discusses the effect of a specific cytokine, interleukin-6 (IL-6), in B-cell lymphomas. IL-6 is a multipotent cytokine that can mediate the differentiation of B-cells into immunoglobulin-secreting cells, stimulate the autocrine or paracrine growth of myeloma cells, induce acute-phase proteins in liver cells, and may influence the pathogenesis of several diseases by autocrine or paracrine mechanisms. Patients with non-Hodgkin's lymphoma (NHL) have increased serum concentrations of IL-6; increased IL-6 levels can be associated with the presence of B-symptoms. Data presented in this review indicate that neoplastic cells from patients with NHL contained high concentrations of IL-6. Thus, elevated serum levels of IL-6 appear to originate from the lymphoma cells in patients with B-cell NHL, suggesting that the neoplastic cells may modulate the general status of patients with B-cell NHL. The inhibition or modification of the production of IL-6 in lymphoma cells may lead to a more effective control of the general status of patients with B-cell NHL.