Chromium picolinate (CrPic, Chromax) is a dietary supplement that is stable and more bioavailable than other commercially available forms of chromium. Chromium supplementation is known to enhance the action of insulin, particularly in insulin resistance and type 2 diabetes mellitus. A previous study reported that CrPic produced increases in mutations of the hypoxanthine phosphoribosyltransferase (Hprt) gene in Chinese hamster ovary (CHO) cell mutation tests. This study, however, evaluated CrPic produced by the testing laboratory and used an atypical 48 h exposure period for this test system. The current study evaluated the mutagenic potential of the most widely utilized commercial form of CrPic in CHO/Hprt mutation tests following International Conference on Harmonisation (ICH) Guidelines (+/-S9 metabolic activation with a 5h exposure) in addition to repeating the test with a 48 h exposure period -S9 activation. CrPic was suspended in dimethyl sulfoxide (DMSO) up to a concentration of 50 mg/mL; exposures were conducted under conditions in which precipitate was not evident and under conditions in which some precipitate of CrPic was visually evident in the cell culture medium at the highest concentrations (500 microg/mL). The concentrations evaluated for mutagenicity ranged from 15.6 to 500 microg/mL (+S9 and -S9) for the 5 h exposure and 31.3-500 microg/mL for the 48 h exposure (-S9). Only a slight degree of cytotoxicity was seen in the standard tests up to the limit of solubility in the medium. Toxicity, i.e., cloning efficiency < or =50% of the solvent control, but no mutagenic increases were observed at 500 microg/mL following a 48 h exposure period. The results of these studies showed that CrPic was non-mutagenic in two independent CHO/Hprt assays and in an assay using a 48 h exposure period.