Daunomycin, like its anthracycline analog adriamycin, is a cardiotoxic antitumor antibiotic. Reports on 5,613 patients receiving daunomycin were reviewed for cardiotoxicity. Two distinct patterns of cardiotoxicity were defined, congestive heart failure (cardiomyopathy) and electrocardiographic changes. Dose-response curves were constructed using the percent incidence of cardiomyopathy versus the total dose of daunomycin in mg/m2. There was a dose-response relationship between the total dose of daunomycin and the development of cardiomyopathy, both in children and adults. The children seem more susceptible to the drug-induced cardiomyopathy. The electrocardiographic changes in the children and adults did not show a dose-dependent relationship, were present consistently even at the lowest dosage levels, and did not predict for subsequent development of cardiomyopathy. The dose-response curves constructed enable the clinician to judge the relative risk of developing cardiomyopathy at a given total dosage level and allows comparison of the human experience with the experimental animal model data.