AbstractThe effects of aspirin on delayed hypersensitivity were assessed in 40 healthy subjects who were randomly assigned to two equal groups. In a double‐blind format, the individuals in one group were placed on 4 gm aspirin daily for 5 days, and individuals in the other group were given placebo. Lymphocyte proliferation was measured before and 72 hours after the initiation of drug, by using three mitogens and four antigens. The percentages of T and B lymphocytes were likewise measured before and during therapy. The subjects were skin tested with the same four antigens 72 hours after the initiation of drug, and the skin tests were read 48 hours later. No significant differences between the two groups were detected when skin tests, lymphocyte proliferation, and percentage of T lymphocytes were compared.