Trivalent chromium (Cr) is now deemed to be an essential trace element. The need to demonstrate a biochemical effect either initiated or augmented by this simple trace element is essential to stimulate interest in its use as a beneficial supplement in diabetes mellitus. For some years our laboratory has contributed to the increasing body of evidence suggesting a role for trivalent Cr in insulin action. We have shown an inverse relationship with plasma Cr and plasma insulin in healthy individuals following a 75g oral glucose load, during hyperinsulinemic euglycemic clamping, and in the presence of postprandial hyperinsulinemia during circadian rhythm studies. These changes are not explained by simple urinary loss alone and suggest the migration of Cr from the blood compartment to tissues. Cr redistribution studies have revealed an association between 51 Cr and insulin-sensitive adipose and striated muscle tissue, but not with insulin-insensitive tissues. These data are consistent with the hypothesis that in vivo Cr translocates from the blood compartment to insulin-sensitive tissues. Using the mouse muscle cell line C 2 C 12 , we have successfully induced an apparent "insulin resistance" in healthy cells by depleting their medium of Cr. Further, we have been able to restore sensitivity to insulin by the addition of physiological levels of Cr. We find that supplementation with Cr can improve sensitivity to insulin in apparently healthy volunteers. Although more detailed studies are required to understand the potential action(s) of trivalent Cr, the possibility that dietary supplementation may conceivably provide assistance to diabetic patients is an increasingly serious consideration.