Coenzyme Q10 (CoQ10) and vitamin B6 (pyridoxine) have been administered together and separately to three groups of human subjects. The blood levels of CoQ10 increased (p < 0.001) when CoQ10 and pyridoxine were administered together and when CoQ10 was given alone. The blood levels of IgG increased when CoQ10 and pyridoxine were administered together (p < 0.01) and when CoQ10 was administered alone (p < 0.05). The blood levels of T4-lymphocytes increased when CoQ10 and pyridoxine were administered together (p < 0.01) and separately (p < 0.001). The ratio of T4/T8 lymphocytes increased when CoQ10 and pyridoxine were administered together (p < 0.001) and separately (p < 0.05). These increases in IgG and T4-lymphocytes with CoQ10 and vitamin B6 are clinically important for trials on AIDS, other infectious diseases, and on cancer.