Rats were given two daily subcutaneous injections of either 40, 80 or 160 mg/kg of glycerol or control injections of glucose. Glycerol injections did not reliably affect body weight gain at any dose tested whether animals were maintained in constant light or a 12 hr light/dark cycle. Only injections of 160 mg/kg of glycerol given twice daily significantly reduced daily food intake; however, this dose also raised plasma glycerol concentrations briefly to an unphysiologic level. Continuous intravenous infusions of 390 or 780 mg/rat/day of glycerol had no effect on food intake, even though plasma glycerol levels increased markedly within the normal range. These findings indicate that reductions of food intake and body weight after administration of glycerol are probably responses to a treatment which is not physiologic.