A great deal of interest in the element vanadium has been generated recently because of its potential as a therapeutic agent for diabetes mellitus. Vanadium's insulin-mimetic properties and its requirement for proper growth and development suggest that it may be involved in insulin's mechanism of action. We have therefore examined vanadium levels in kidney, muscle, and liver tissues from normal and diabetic BB Wistar rats. Our results indicate that diabetes mellitus can decrease the tissue vanadium content of liver, suggesting that the trace element vanadium may be important in insulin action.