Persons involved in the study, 21 per treatment arm, were consuming ubiquinone (Q10), 90 mg/day, 180 mg/day or placebo, for two weeks prior to hepatitis B vaccination. After 30 days this vaccination was repeated. Q10 was given as soft gelatin capsules containing 30 mg each. The consumption was continued throughout the study conducted for 90 days. Clinical observations and laboratory tests were performed throughout the study and no adverse effects were observed in any of the groups. Already after 30 days the two groups receiving Q10 showed a slightly titer of antibodies to hepatitis B surface antigen then the placebo group. This difference escalated and the immunopotentiating effect of Q10 was even more clear-cut in the residual part of the study. In addition, a dose response did also seem to be present when comparing the 90 mg group with the 180 mg group. Statistics revealed that Q10 in the dose 180 mg/day is able to increase antibody response in vivo in humans vaccinated against hepatitis B with up to 57% (p = 0.011).