Therapy with a pharmaceutical formulation of coenzyme Q.sub.10 (CoQ.sub.10) of patients with Acquired Immune Deficiency Syndrome, known by the acronym AIDS and of patients with other retroviral diseases including the AIDS-related complex known as ARC is useful to reduce or negate opportunistic infections, adenopathy and other undesirable clinical symptoms. CoQ.sub.10 therapy may be used in conjunction with antibiotic therapy to prevent or suppress secondary opportunistic infections.