Oral administration of the contact sensitizer oxazolone to normal mice produced tolerance rather than skin sensitivity. Under certain conditions, oral dosing of skin-sensitized mice produced a temporary depression in the response to skin challenge. Oral or rectal challenge of skin-sensitized mice failed to elicit an allergic reaction in the intestinal mucosa. The results are discussed in relation to the hypothesis that the lymphoid cell population in the intestinal epithelium is involved in cell-mediated immunological reactions.