Bumetanide, a pharmacologically new diuretic, was evaluated in 27 subjects. Its onset of action was within 30 minutes with a peak at 90 minutes and a total duration of action of about 270 minutes. In a controlled study in oedematous patients it was equipotent with frusemide at one-fortieth the molar dosage and did not differ from frusemide with regard to its pattern of electrolyte excretion. On continuous oral administration for eight days it produced effective diuresis with minimal alteration in biochemical and haematological status. The only adverse effect was gastric discomfort in one patient.