The efficacy of 1 mg bumetanide on nocturia was compared with placebo in a randomised double-blind cross-over study in general practice. Twenty-eight patients, 13 females and 15 males, completed two treatment periods of 2 weeks' duration. During the placebo period the weekly number of nocturia episodes was 13.8 and during bumetanide treatment the number was reduced by 3.8. Ten males had a history of prostatic hypertrophy and in these patients treatment with bumetanide was not beneficial. In the remaining 18 patients the weekly number of nocturia episodes was reduced by 4 during bumetanide treatment compared with the placebo period. Of these patients, 3 preferred treatment with placebo, 11 preferred bumetanide and 4 gave no preference. These results suggest that bumetanide offers an alternative in the treatment of adult nocturia not connected with enlargement of the prostate.