The effect of beta 1 and beta 2 blockade on dopamine and dobutamine induced hypokalaemia was investigated in dogs. Arterial plasma potassium was continuously monitored using a potassium-sensitive electrode sited in the abdominal aorta. Dopamine and dobutamine were infused at 15 micrograms kg-1 min-1 into animals pre-treated with atenolol (0.5 mg kg-1) or ICI 118551 (0.5 mg kg-1) and the potassium changes compared to those seen in control animals. The inotrope infusions caused a small and transient rise in plasma potassium (p less than 0.05) followed by a more profound hypokalaemia (p less than 0.05) sustained for the duration of the infusion. The potassium falls in the control animals were similar to those in the beta 1 and beta 2 blockade groups. The results suggest that beta 2 receptor stimulation cannot alone be responsible for dopamine and dobutamine induced hypokalaemia and a multiple receptor activation is postulated.