Cytotoxicity of ammonium metavanadate to cultured bovine pulmonary alveolar macrophages was measured by cell viability, inhibition of phagocytosis, and reduction of superoxide‐dependent chemiluminescence. The degree of toxicity was dependent on the levels of vanadium, the temperature, and the time of exposure. Thus macrophages exposed to vanadium at 0.01 and 0.1 μg/ml did not exhibit cytotoxic effects even with up to 24 h of exposure, as measured by cell viability and phagocytic index. Vanadium at 0.5 μg/ml, however, reduced cell viability to 24% and the phagocytic index to 2% of the control within 8 h of exposure. Exposure to NH4VO3(up to 1 μg vanadium/ml) for short periods of time stimulated phagocytic activity. Vanadium toxicity was also demonstrated in suspension culture at 37°C by chemiluminescence assay. This assay seems to be more sensitive than the conventional viability and phagocytic index tests. Thus, the peak light production by macrophages during zymosan phagocytosis was reduced to 93, 59, and 63% by vanadium at 0.1 μg/ml exposing for 2, 4, and 8 h, respectively, and to 71, 27, and 24% by vanadium at 1.0 μg/ml for the same time periods. The phagocytic activity of macrophages as measured by chemiluminescence response was not significantly altered by exposure to either 0.1 or 1.0 μg vanadium/ml measured during the first 24 h of culture at 4°C.