A prospective study of 11 cases of Clistanthus collinus leaf poisoning was undertaken to evaluate the mechanism of hypokalaemia that occurs in these cases. Continuous cardiac monitoring was done. Ventricular ectopics, ventricular tachycardia and fibrillation were the important arrhythmias. No atrioventricular blocks or other significant bradyarrhythmias were noted. The renal potassium loss was found to be very high (120 +/- 87.95 mEq/L) even in the presence of hypokalaemia and in spite of continuing drop in serum potassium concentration. Metabolic study established that renal potassium leak is the mechanism by which hypokalaemia was mediated.