The effects of aspirin and bendrofluazide alone and in combination were studied on the diuresis, natriuresis, kalliuresis and excretion of salicylates in normal human volunteers. The simultaneous administration of both drugs in a sequence of aspirin-bendrofluazide was accompanied by a reduction in the kalliuretic effect of aspirin without any significant effects on the natriuresis, kalliuresis and diuresis induced by bendrofluazide. Concomitant administration of both drugs produced marked increases in the amount of salicylate excreted over the experimental session, being highest (58.3%) with an aspirin-bendrofluazide sequence, and lowest (30.3%) when injected simultaneously (suggesting antagonism by bendrofluazide). The results suggest interference by bendrofluazide with the excretion of salicylate but not vice versa.