The myocardial lesions induced in rabbits by the administration of daunorubicin (total cumulative dose 19.2 mg/kg) over a period of 15 weeks remained stable over a 3 month period after cessation of therapy. Such lesions were markedly reduced by pretreatment with 25 mg/kg of ICRF-187, and failed to increase in severity during the 3 month post treatment period of observation. Thus it was concluded that ICRF-187 does result in reduction of these lesions rather than just in a delay in their appearance.