Background: In a previous study it has been shown that acupuncture activates the respiratory burst (RB) of neutrophils as measured by the differences to baseline of the mean channel number of fluorescence intensity (mfi) in volunteers. Since this result could have been affected by a placebo effect, a study has been designed that controls for the different facets of placebo mechanisms such as expectancy, suggestibility, and conditioning. Participants and Methods: 60 healthy volunteers were randomized either to acupuncture of the acupoint Large Intestine 11 (LI 11) (groups 1 and 2) or relaxation (group 3) twice a week for 4 weeks. Only acupuncture group 1 and the relaxation group were provided with the additional suggestion that the treatment may strengthen the immune system. Results: The repeated measurement analysis for differences of follow-ups to baseline showed significantly different treatment effects for neutrophils but not for monocytes (unprimed neutrophils: p = 0.004; neutrophils primed with TNF-alpha/FMLP or with FMLP only: p = 0.026 and p = 0.019, respectively) between groups. For both cell types post-hoc Dunnett’s t-tests using the relaxation group as control showed significantly stronger treatment effects for acupuncture group 1. Combining all priming procedures, the average increase in mfi for both cell types was about 30% greater in acupuncture group 1 than in the relaxation group. Plasma concentrations of pro-inflammatory cytokines only increased significantly in the acupuncture groups. Conclusion: Repetitive acupuncture increases the cytotoxicity of leukocytes in healthy volunteers, which might be intensified by a conditioning-expectation effect.