Glucose uptake was measured by a noninvasive fluorescence technique on a total of 165 morula- and blastocyst-stage murine embryos in two different culture media. Eighty-four embryos were tested in M2 medium, and the remaining 81 embryos were tested in M16. Embryos assayed in M2 took up significantly less glucose over the 4-h assay period than did embryos assayed in M16. The lower uptake of glucose by embryos in M2 corresponded with a decrease in the quality of embryos cultured overnight in M2 as judged by morphological criteria. Embryos that were judged to be degenerate or had gross abnormalities took up significantly less glucose than did normal embryos. Glucose uptake in both populations of embryos covered a wide range of values and was normally distributed. A significant effect between mothers was noted in glucose uptake for embryos assayed in both M16 and M2 media. The possible uses of noninvasive measures of glucose uptake as a test of embryo viability or for optimizing culture conditions are discussed.