To investigate effects of doxorubicin therapy on cardiac electrophysiology, with special emphasis on QT dispersion and late potentials, in lymphoma patients. Prospective study. University hospital. Twenty-eight adult non-Hodgkin's lymphoma patients who received doxorubicin to a cumulative dose of 400-500 mg m-2. Standard 12-lead electrocardiogram (ECG) and signal-averaged ECG (SAECG) recordings were performed at baseline and after cumulative doxorubicin doses of 200, 400 and 500 mg m-2. Heart rate-corrected QT interval (QTc) increased from 402 +/- 4 to 416 +/- 5 ms (P = 0.002) during the study period. QT dispersion (variability in QT interval duration amongst the different leads of the standard 12-lead ECG) increased from 24.1 +/- 2.5 to 35.0 +/- 2.8 ms (P = 0.041) and QTc dispersion increased from 26.5 +/- 2.5 to 39.0 +/- 3.5 ms (P = 0.039). Five patients (18%) developed QT dispersion exceeding 50 ms. In addition, two patients (7%) developed late potentials during doxorubicin therapy. The changes in QTc duration, QT dispersion and late potentials occurred independently of the impairment of left ventricular function. Prolongation of QTc, increased QT dispersion and development of late potentials are indicative of doxorubicin-induced abnormal ventricular depolarization and repolarization. QT dispersion and late potentials are both known to be associated with increased risk of serious ventricular dysrhythmias and sudden death in various cardiac diseases. Thus, follow-up of these parameters might also be useful in assessing the risk of late cardiovascular events in cancer patients treated with anthracyclines.