Vanadium (V) is an element with wide industrial applications and environmental release. The object of this study was to determine the in vitro effects of high (10(-4) M) and low (10(-7) M) concentrations of sodium metavanadate (NaVO3) on cultured peripheral blood mononuclear cell (PBMC) proliferation, cytokine release, CD expression, and granulocyte O2- production. At 10(-4) and 10(-7) M, NaVO3 did not modify PBMC proliferation in the absence of phytohemagglutinin (PHA). On the other hand, 10(-4) M NaVO3 reduced by -25% the PBMC proliferation in PHA-stimulated cultures, with a significant reduction of the stimulation index (SI) of blastogenesis. Moreover, 10(-4 M NaVO3 significantly reduced the release of IFN-gamma by PHA-stimulated PBMCs, and 10(-7) M NaVO3 significantly enhanced the release of TNF-alpha. In addition, IL-5 release was significantly inhibited by high concentration of sodium metavanadate and significantly enhanced by low concentration of NaVO3. Neither 10(-4) nor 10(-7) M NaVO3 modified the expression of CD3+, CD4+, CD8+, or CD56+ in PHA-stimulated and unstimulated lymphocytes. Finally, 10(-4) M NaVO3 reduced the granulocyte production of O2- by about 70%, while 10(-7) vanadate reduced its production to a lesser extent. These results show that 10(-4) M NaVO3 exerts inhibitory effects on PBMCs, while at 10(-7) M it exerts a stimulatory action with a slight shift of the immune response towards a Th2-type response. This investigation suggests that environmental V can have important effects on the human immune system.