Toxicity of high-dose cytosine arabinoside in the treatment of advanced childhood tumors resistant to conventional therapy. A Pediatric Oncology Group study. Experience with high-dose cytosine arabinoside (HDAC) in pediatric solid tumors is limited. Sixteen children with solid tumors resistant to conventional therapies were registered in a pilot Pediatric Oncology Group (POG) study that required the administration of HDAC at 3 g/m2 every 12 hours for four doses. There were four cases of rhabdomyosarcoma, two cases of fibrosarcoma, four cases of neuroblastoma, and one case each of germ cell tumor, Wilm's tumor, retinoblastoma, hepatocellular carcinoma, Ewing's sarcoma, and Burkitt's lymphoma. All eligible patients had advanced diseases and had previously received extensive chemotherapy. Thirteen patients received one course of HDAC and three patients received two courses of HDAC. Due to prior treatments, patients had less than normal marrow reserves. Short-term toxicity included nausea, vomiting, suppression of hemopoiesis, drug fever, and increased blood urea nitrogen (BUN), creatinine, and liver enzymes. All evaluable patients recovered from their toxicities. There were no drug-related deaths. None of the patients had neurologic problems, including the only patient with prior irradiation to the skull. With the above schedule, HDAC appears to have manageable toxicity. 