It has been shown that acupuncture can modify circulating levels of subpopulations of leukocytes. There have been few investigations on the effect of acupuncture on prostaglandins metabolism. Aspirin is capable of inhibiting the metabolism of prostaglandins and to produce several pharmacological effects. The objective of this study was to determine whether prior administration of aspirin could modify the action of acupuncture on levels of circulating leukocytes. Fourteen healthy males (age: 19-23 years) were recruited from a university student population. This study was a placebo-controlled, prospective, cross-over design. Subjects were randomly assigned into A or B groups. Group A received aspirin 500 mg and group B placebo, after 1 week of a washout period, group A received placebo and group B aspirin. Subjects were given acupuncture with manual needling in GV14 (Dazhui) acupoint 2 hr after receiving medication. The needle was stimulated for 10 sec and was kept in place for 5 min. Leukocytes and their subpopulations were quantified in blood samples taken immediately before and 2 hr after acupuncture treatment. In each subject pre-acupuncture values were compared to those post-acupuncture. The results showed that acupuncture significantly increased overall leukocytes (p=0.006) and neutrophils (p<0.001). Aspirin partially inhibited these effects. The data suggest that the effect of acupuncture on leukocytes may be related to levels of prostaglandins.