Objective: This study was conducted to assess the effect of acute lymphoblastic leukaemia as a disease and cytotoxic therapy on serum levels of total immunoglobulin G and immunoglobulin G subclasses (G1, G2, G3, G4), with IgA, IgM,complements C3, C4 and vitamin E (as an endogenous antioxidant) in children with acute lymphoblastic leukemia. Subjects and Methods: Twenty-six children with acute lymphoblastic leukemia completed the study, which was conducted in the Hospital of Nuclear Medicine in Mosul city from Jun 2005 to Apr 2007. Also included in the study a 27 apparently healthy age and sex matched children serve as a control for the initial laboratory results. Initially for both the patients and controls, a blood sample withdrawn and serum total immunoglobulin G, subclasses (G1, G2, G3, G4), immunoglobulin A, immunoglobulin M, complements C3, C4 and vitamin E was measured (immunoglobulin groups, and subclasses of IgG with the complements C3,C4 using radial immunodiffusion methodology with specific kits, while serum vitamin E was measured by high performance liquid chromatography). For the patient’s group the same parameters were measured after receiving the cytotoxic therapy for the induction remission and consolidation phases of therapy.