Recognition of adverse late cardiac effects from cancer therapy may enable identification of patients with risk of cardiotoxicity upon cancer retreatment. In this study the feasibility of using iodine-123 metaiodobenzylguanidine (123I-MIBG) heart scintigraphy to detect abnormalities of the myocardial adrenergic neurone function in the late period after cancer therapy was evaluated in relation to the left ventricle ejection fraction (LVEF) in 18 cancer patients: 11 had undergone thoracic irradiation involving the heart, in five cases in combination with anthracycline therapy, 11-228 months (median 60 months) before radionuclide tests, while seven had not received previous anthracycline and/or radiotherapy (controls). The 123I-MIBG cardiac uptake, expressed as a heart-to-mediastinum ratio on planar images after 4h, ranged from 1.21 to 1.76 (median 1.56) in cancer therapy patients, which was significantly decreased (P=0.0006) in comparison with controls (range 1.81- 2.06, median 1.9). The myocardial 123I-MIBG washout, calculated from planar images after 15 min and 4 h, and LVEF also showed significant differences, but with some overlap in individual cases. In cancer therapy patients, cardiac abnormalities seen on planar images and additional single-photon emission tomographic images varied from focal defects to diffusely reduced myocardial uptake. It is concluded that 123I-MIBG heart scintigraphy, which is able to identify cardiac adrenergic neurone abnormalities in the follow-up period after cancer therapy, may help to identify relapsed patients who are at increased risk of developing cardiotoxicity during retreatment with cardiotoxic therapy modalities.