1. Infusion of salbutamol (3.0 microgram/min after a bolus injection of 100 microgram) produced hypokalaemia in conscious dogs. 2. Measurement of arterial and coronary sinus potassium differences revealed no significant potassium loss from the heart with established hypokalaemia. 3. Shortly after the initial salbutamol bolus and before steady-state hypokalaemia had been achieved during salbutamol infusion, a prolongation of QTc occurred; this corresponded to a significant myocardial potassium of -0.12 mmol/l plasma. 4. Urinary electrolyte excretions indicated that the hypokalaemia was not due to urinary potassium loss. 5. It was deduced that potassium had moved intracellularly. No change in hydrogen ion status occurred to account for this. Pronounced rises in plasma insulin immunoreactivities during salbutamol infusions suggested this as one mechanism for potassium shifts.