Out of a total of 126 patients with acute lymphoblastic leukemia, including 69 children aged less than 15 years, and 57 adults aged less than 60 years, who were treated with daunomycin (D.N.R.) initially and with several courses of reinduction, we noted 4 cases of decompensated heart failure (3.1%). 3 cases occurred in children aged 4, 5 and 5 years, and in the last case, in a young adult, of 19 years. Three of these patients were in complete remission of the blood and were only undergoing courses of reinduction. The 4th was in incomplete remission. When symptoms first occurred, about 2 months after the last injection of D.N.R. the total dose administered varied between 14 and 31 mg/kg, extending over periods of 5 to 16 months (average monthly dose 1.9 to 2.8 mg/kg). Except in one case, the course only mildly influenced by the symptomatic treatment and death occurred in 3 patients within from 15 days to 5 months after the onset of the first symptoms. The last patient is still alive and seems stabilised with a follow up period of 9 months. The responsibility of D.N.R. in the development of this myocarditis appears very likely. The unforeseable character of such complications, which are independent of age, and not necessarily linked to any excessive dosage, should be taken into consideration in the indications for D.N.R. in spite of their relative rarity.