Since autocrine stimulation by tumor necrosis factor-alpha (TNF alpha) may be implicated in the proliferation of normal and malignant B cells, we measured the production of TNF alpha protein by these cells in response to various B-cell stimulatory agents. Purified malignant and non-malignant B lymphocytes were incubated with interleukin-4 (IL4), interferon-alpha (IFN alpha) and IFN gamma, and the supernatants were tested for the production of TNF alpha using an enzyme-linked immunosorbent assay (ELISA). Chronic lymphocytic (CLL) and prolymphocytic (PLL) leukemia cells produced low amounts of TNF alpha, irrespectively of the addition of inducers. Normal B lymphocytes (tonsillar and blood) produced TNF alpha, but the level was not influenced by any of the inducers tested. Hairy cell leukemia (HCL) cells produced TNF alpha in the absence of stimuli and this production was markedly enhanced by addition of IFN alpha or, to a lesser extent, by IFN gamma and IL4. These results contradict the hypothesis that IFN alpha exerts its therapeutic action in HCL by inhibition of autocrine TNF alpha production.