Polyoxyethylene mono- and di-stearates, mono- and dioleates, and mono- and di-laurates were fed to groups of rats at a level of 6% of the diet. Polyoxyethylene-8-monostearate (Myrj 45) was fed to rats and cats at levels of 10% and 20% of the diet, respectively. The polyoxyethylene moiety of Myrj 45 was fed to rats at a dietary level of 6%. These experiments were of the long-term type extending over one and a half years for the rats and over one year for the cats. At the end of the experiment the animals were autopsied and the spleen, liver, lungs, testes, thyroid, adrenal, kidney, intestine, urinary bladder and heart were removed for preparation of tissue sections and histological examination for possible evidence of pathology. There were no significant differences between the groups fed the control diets and those given the same diets supplemented with these various polyoxyethylene esters. It is concluded that under the experimental conditions employed, no reasonable doubt exists concerning the safety of the polyoxyethylene stearates even when fed at levels up to 20% of the diet. The low palatability of these compounds together with the fact that the polyoxyethylene moiety has no nutritive value renders impractical their usefulness at anything but low levels.