The purpose of this study was to determine what effect the usual dosage of acetylsalicylic acid (aspirin) would have on the normal pattern of cold defense in man. Seven subjects participated in the experiment, with three exposures per subject conducted at 4° C. Subjects received ten grains of aspirin in one exposure and a ten-grain placebo in the second; the third exposure was a control with no capsule given. Results of these exposures are shown in graphs of skin and rectal temperatures. A discussion of the results is presented. The usual dosage of acetylsalicylic acid in itself appears to have no significant effect on the normal pattern of cold defense in man. There was a psychogenic reaction when a placebo or aspirin was administered.