We describe two patients who develop torsades de pointes in a temporal relationship to the intravenous administration of erythromycin lactobionate in the absence of other drugs or metabolic abnormalities known to cause the arrhythmia. We also review the current literature regarding this topic, including other case histories and the evidence for erythromycin's effect on cardiac tissue. Due to the increasing use of erythromycin in clinical practice, we believe it is important that all physicians be made aware of this potential complication, which was not recognized at our institutions until these patients were seen by one of us (B.G.).