The antisecretory activity of nizatidine, an H2-receptor antagonist, has been extensively investigated in man both by quantitative acid secretory tests and by means of 24-h continuous ambulatory pH monitoring. Studies have shown that nizatidine is a potent inhibitor of basal, nocturnal and stimulated acid secretion. Particular modalities of nizatidine administration, such as early evening intake with supper or morning dosing, have been recently defined. Further studies are needed to clarify if rebound nocturnal acid hypersecretion may develop after abrupt withdrawal of nizatidine or if tolerance may develop during prolonged administration.