The production of interleukin-1 (IL-1) and tumor necrosis factor (TNF) by tumor-associated mononuclear leukocytes (TAML) and peripheral mononuclear leukocytes (PMBL) from 9 otherwise untreated patients with a variety of malignancies (lung, sarcoma, stomach, renal) was assessed. Cells were cultured for 24 hr in vitro in the presence or absence of lipopolysaccharide (LPS), and IL-1 and TNF levels were measured in culture supernatants. TNF production was comparable between TAMLs and PBMLs. However, a striking defect in IL-1 production by TAMLs was noted. There was no basal production of IL-1 and LPS-stimulated TAMLs produced only 1% the amount of IL-1 produced by LPS-stimulated PBMLs.