The relationship between immunotoxicity of ammonium metavanadate (NH4VO3) and levels of tumor necrosis factor-alpha(TNF-alpha) and interleukin-1 (IL-1) was studied with a NH4VO3-treated murine macrophage-like cell line, J774 and resident peritoneal macrophages (PEM) obtained from treated mice. Lipopolysaccharide (LPS)-induced elevation of extracellular TNF-alpha in PEM and J774 cells was not markedly affected by prior treatment with vanadate. However, PEM from treated mice at 10 mg V/ kg (10V) had a significantly lower level of LPS-induced intracellular TNF-alpha. NH VO-treated J774 cells at 3.6 (V1) and 437.2 mug V/107 cells (V2) had significantly higher levels of intracellular TNF-alpha than the PO4 and V3 (10.8 mug V/107 cells) groups. Although the four PEM groups showed no marked difference in extracellular IL-1 levels, PEM from treated mice at 2.5V and 10V had significantly lower levels of intracellular IL-1 than those from control groups. J774 cells from PO4 and NH4Cl groups showed significant increases in intracellular IL-1 following treatment with LPS. However, J774 cells with prior treatment with vanadate revealed significant reduction in levels of LPS-induced intracellular IL-1 when compared to control groups. Therefore, the previously reported reduced resistance of vanadate-treated mice to Listeria monocytogenes could be attributed to an inhibitory effect on the production of IL1 in macrophages.