The effects of chromium compounds on 3-O-methylglucose (3-O-MG) transport were studied in isolated rat adipocytes. Sodium chromate significantly stimulated 3-O-MG uptake into adipocytes in a dose-dependent manner without altering the equilibrium space of 3-O-MG in adipocytes. The stimulatory effect reached the maximum at 300 microM, and the effect was 60-70% of the maximal insulin effect that was obtained with 20 nM insulin. The chromate concentration achieving a half-maximal effect was estimated at 50 microM. The effect of the combination of 1 mM chromate and 20 nM insulin was equipotent to that of 20 nM insulin alone, which showed that these two effects were not additive. The stimulatory effects of 1 mM chromate and 20 nM insulin were entirely abolished in adipocytes deprived of ATP, which indicated that these effects were completely ATP-dependent. Judging from experiments using various chromium compounds, CrO4(2-) was responsible for the insulinomimetic action. These results indicate that the action of CrO4(2-) is exerted through a mechanism analogous to that of insulin action, and that CrO4(2-) is a novel and useful tool for studying issues involved in insulin actions.