The effect of coenzyme Q10 on glioma-cell proliferation under serum-deprived conditions has been studied. Our results have shown that the addition of coenzyme Q10 into a serum-free culture medium enhances cell viability, stimulates cell growth, restores mitochondrial potential, and increases the quantity of energized mitochondria. It is found that coenzyme Q10-induced glioma-cell proliferation in conditions of serum deficiency is a result of an intracellular reduced glutathione concentration with subsequent activation of protein kinase C, ERK1/2, and phosphoinositol-3-kinase.