BACKGROUND AND PURPOSE To assess the ability of children with acute lymphoblastic leukemia (ALL) to develop an antibody response after influenza vaccination. METHODS A total of 65 children under 15 years old were studied, including 25 children with ALL undergoing chemotherapy, 30 with asthma in remission who were regularly followed at clinics, and 10 healthy children. The influenza vaccine contained antigens B/Yamanashi/166/98, A/New Caledonia/20/99 (H1N1), and A/Panama/2007/99 (H3N2). RESULTS Children with ALL developed significant antibody titers to A/Panama /2007/ 99 antigen 4 weeks after the second immunization. Seroconversion rates after two doses of vaccine were 57.1 to 84.6% and seroresponse rates were between 24 and 60% in children with ALL. Compared to children with asthma in remission, who were regarded as immunocompetent individuals, the ALL children had less seroconversion and lower seroresponse rates to A/New Caledonia/20/99 (H1N1). The seroconversion and seroresponse rates to B/Yamanashi/166/98 and A/ Panama/2007/99(H3N2) antigens were comparable in asthmatic and leukemic children. On the other hand, the antibody response in children with ALL who received reinduction chemotherapy suggests that the therapy did not impair seroresponse rates. CONCLUSION Our data suggest that the influenza vaccine is safe and effective in children with either ALL or asthma in Taiwan.