Background. Children with cancer receiving intensive chemotherapy require multiple transfusions and are at increased risk for blood transmittable diseases such as hepatitis B virus (HBV), hepatitis C virus (HCV), and human immunodeficiency virus (HIV) infections. Procedure. Sera from 50 children (24 female, 26 male) admitted between January, 1994, and December. 1995, with solid tumors receiving intensive chemotherapy and multiple transfusions were investigated for HBsAg, anti-HBs, anti-HBc, anti-HCV, and anti-HIV by ELISA at diagnosis and at the end of therapy. Results. HBsAg, HBV, HCV, and HIV seropositivities were 0%, 4%, 2% and 0% at diagnosis and 10%, 20%, 14% and 0% at the end of therapy, respectively. Conclusions. The high seroprevalence of HCV may be due to the lack of anti-HCV screening of blood products in the blood banks during the study period. Although the HBV seroprevalance of 20% found in this study is much lower than the value of 56% found in a previous study conducted during 1986-1989 in a similar patient population and a similar setting, it is still high. Children infected with HBV during immunosuppressive therapy are at greater risk of becoming chronic carriers and precautions must be taken for immunization of these children. Med. Pediatr. Oncol. 34:102-105, 2000. (C) 2000 Wiley-Liss. Inc.