† Retinoblastoma in 50 children between the ages of 2 months and 7 years was treated by a combination of radiotherapy and triethylene melamine. This series included only cases in which the disease had not extended beyond the local area. The usual dosage of radiation was 2,400 r in air through each of two portals. The drug was given by mouth originally and later by intramuscular injection, or by instillation into the internal carotid artery, the dosage being adjusted according to the weight and hematological response of the patient. The tumor was arrested and vision preserved, as judged from subsequent observation over a period of at least six months, in 12 out of 33 children who received the drug by mouth. Arrest of tumor growth and retention of useful vision was achieved in seven of eight children who received the drug intramuscularly. The intracarotid route was used in nine far advanced cases that had been classified as "almost hopeless"; in this group the tumor was arrested and useful vision preserved in two cases. The results have been better than those obtained in the past in comparable series with radiotherapy alone. Therapeutic doses of triethylene melamine produce hematological depression, and complete blood cell and platelet counts are a necessary and useful guide to the dosage and prevention of potentially severe toxic reaction in these cases. Given by mouth, the drug produced the maximum leukopenia in about nine days; given intramuscularly, it required about half that time. The latter route is definitely preferred.