The authors investigated in a group of 106 patients with a first myocardial infarction treated by thrombolysis the effect of i.v. administration of creatine phosphate (a new drug with cardioprotective action--Neoton Alfa Schiapparelli Wassermann Co). In the course of treatment electrocardiographic changes were recorded and the presence of arrhythmias examined by the Holter technique. The Neoton group displayed a statistically insignificant but nevertheless obvious trend of electrocardiographically less serious forms of infarction and a lower incidence of infarctions, as compared with the control group.