Vitamin C status and total antioxidant capacity (TAC) in children with acute lymphoblastic leukemia (ALL) was assessed in 28 hospitalized patients and 30 apparently healthy control subjects. It was determined that whereas vitamin C intake in patients with ALL was more than twice as much as in controls, plasma and urinary concentrations of vitamin C were more than 10 times and 2.5 times higher in controls than in the patients with ALL, respectively (P < 0.001). Accordingly, serum TAC levels in the patients with ALL were lower than in healthy subjects (P < 0.001). Vitamin C utilization is increased in children with ALL.