Doxorubicin is one of the most effective antineoplastic agents but its limited use is due to acute and chronic cardiotoxicity. These side-effects are irreversible and dose-dependent, occurring in one-third of the patients treated after a cumulative dose of 300 mg/m2. It has been suggested that the problem of acute and chronic cardiotoxicity may be prevented by using L-carnitine. Hence nine patients receiving a cumulative dose (200-490 mg/m2) of doxorubicin have been studied. Acute cardiotoxicity has been evaluated by creatine kinase---marsh bender (MB) serum levels before and 15 h after treatment. Data demonstrated no significant increase of isoenzyme-MB after doxorubicin administration. Chronic cardiotoxicity has been monitored studying the electrocardiograph and the left ventricular performance by computerized M-Mode echocardiography measuring the maximal velocity of circumferential fibre shortening (VCF Max) which is considered a reliable and very sensitive non-invasive parameter to evaluate myocardial contractility. The results show a decrease in VCF Max (measured in diameter/cardiac cycle) from 1.7 +/- 0.4 to 1.4 +/- 0.3 but still within normal values. So the systematic use of L-carnitine as adjuvant therapy is proposed during doxorubicin administration.