Endomyocardial biopsy was done 119 times in 98 patients receiving doxorubicin therapy once every 3 weeks and 41 times in 27 patients receiving doxorubicin therapy weekly. Factors contributing to the degree of anthracycline-induced endomyocardial injury were evaluated. Neither age, sex, type of malignancy, concomitant use of other chemotherapeutic agents including cyclophosphamide, nor history of cardiac disease or hypertension influenced the extent of the endomyocardial injury. The dose of doxorubicin (p = 0.0001) and the schedule (weekly versus 3 weekly) (p = 0.0020) independently predicted the degree of endomyocardial damage in multivariate analyses. Previous cardiac irradiation had borderline significance (p = 0.074) in predicting endomyocardial damage in this analysis. Doxorubicin therapy administered on a weekly schedule is associated with less anthracycline-induced cardiac damage than is doxorubicin therapy delivered in the conventional, 3-weekly schedule.