Coordination complexes of chromium (Cr) and two pyridine carboxylate isomers, nicotinate (nic) and picolinate (pic) were synthesized and analyzed. Cr mono and dinicotinate complexes were formed with 1:1 and 1:2 ratios of Cr3+ and nic at pH 7.5. Cr dinicotinate was the only complex formed from a 1:3 ratio of Cr3+ and nic. Mono, di, and tri picolinate complexes were formed with 1:1, 1:2, and 1:3 ratios of Cr3+ and pic at pH 7.5. Cr is coordinated with nic through the carboxyl carbon while Cr is coordinated with pic through both the pyridine nitrogen and the carboxyl carbon. Cr dinicotinate enhanced insulin activity in isolated adipose tissue. None of the other complexes were active in this assay system. In contrast, Cr tripicolinate, which is lipophilic, increased glucose uptake by skeletal muscle cultures but none of the other complexes were effective. In addition, dietary supplements of Cr tripicolinate increased rate of lean body mass development in humans and decreased hemoglobin glycation in aging rats. None of the other complexes was effective in these in vivo assays. The results of this investigation prove that the chemical properties of Cr nic and Cr pic complexes differ markedly. The chemical differences result in a vast difference in the biological action of the complexes.