We examined the TNF-alpha activity in culture supernatants of monocytes isolated from the peripheral blood of patients with SLE and of normal individuals. The monocytes from patients with SLE stimulated with silica particles, lipopolysaccharide or Staphylococcus aureus Cowan 1 secreted significantly lower amounts of TNF-alpha than did normal monocytes. A decreased TNF mRNA expression was observed in peripheral blood mononuclear cells stimulated by mitogens from patients with SLE. Furthermore, we examined the effect of recombinant TNF-alpha (rTNF-alpha) on the B cell function in SLE patients. rTNF-alpha inhibited the spontaneous B cell proliferation of SLE, but tended to enhance the normal B cell proliferation. Spontaneous IgM production from SLE B cells was inhibited by rTNF-alpha, but that from normal B cells was not. Spontaneous IgG production was unaffected by rTNF-alpha. Also, rTNF-alpha did not affect the viability of B cells. These findings suggest that an impaired TNF-alpha production and an abnormal B cell response to TNF-alpha play a role in the immunological dysfunction in patients with SLE.