In a patient with renal failure and shortness of breath, Q waves transiently appeared in the right precordial leads of the electrocardiogram (ECG) during episodes of hyperkalemia, without a substantial change in mean electrical axis. With restoration of the plasma potassium level to normal, R waves reappeared in these leads. It is concluded that the transient development of Q waves in the right precordial leads during hyperkalemia resulted from a hyperkalemia-induced conduction disturbance. Hyperkalemia, by affecting conduction in Purkinje fibers of ventricular muscle, or both, disturbed the normal sequence of septal and anterior wall depolarization and resulted in an ECG pattern that mimicked that of anteroseptal myocardial infarction. Clinically, hyperkalemia-induced conduction disturbances of this type must be included in the differential diagnosis of the ECG that suggests an anteroseptal myocardial infarction.