Female B6C3F1 mice were injected intraperitoneally with ammonium metavanadate (2.5 or 10 mg V/kg), ammonium chloride, or sodium phosphate buffer (0.1 M, pH 7.2) every 3 d for 6 wk. Resident peritoneal macrophage (PEM) cytolysates were prepared and assayed for intracellular enzyme activities of beta-glucuronidase, N-acetyl-beta-D-glucosaminidase, acid phosphatase, and lysozyme, to investigate possible reasons for the depressive effect of ammonium metavanadate on the intracellular killing of Listeria monocytogenes by murine PEM. Acid phosphatase activity per 10(6) cells for the 2.5 and 10 mg V/kg groups was depressed by 22.8 and 44.7%, respectively, when compared to phosphate buffer controls. No significant effect by vanadium treatment was observed with regard to the other three enzymes. Kinetic studies (in vitro) on the effect of ammonium metavanadate (5, 10, 15, and 20 mM) on the above enzymes showed similar patterns of effect by vanadium. Lineweaver-Burk analysis of acid phosphatase indicated linear noncompetitive inhibition by vanadium with a Kj of 14.8 mM. NH4Cl and 10 mg V/kg treatments also enhanced extracellular secretion of beta-glucuronidase and lysozyme from PEM, which could be attributed to the presence of ammonium ion. The decrease in acid phosphatase activity might contribute, in part through its interference in the phosphorylation/dephosphorylation, to the diminished intracellular killing ability of PEM.