Since the incidence of peptic ulcer and gastroesophageal reflux (GER) is more common in patients with chronic obstructive pulmonary disease (COPD) than normal population, H(2) receptor blockers are given more extensively to COPD patients. This study evaluated the effects of Ranitidine on pulmonary function tests (PFT) of the patients having COPD and peptic ulcer or GER, and of healthy volunteers. Fifty milligrams of Ranitidine was given intravenously to 30 COPD patients and 25 healthy volunteers. PFT were done before and 15, 30, 60, 120min after Ranitidine injection. Although mean forced vital capacity (FVC), forced expiratory volume in 1s (FEV(1)) and forced midexpiratory flow rate (FEF(25-75%)) of COPD patients were found to be decreased 60 and 120min after Ranitidine injection, the decrements were statistically insignificant. The decrements in PFT of healthy volunteers were also not statistically significant.H(2) receptor blockers can be used safely for treatment of gastrointestinal disorders in COPD patients who have mild or moderate obstruction. Minimal decreases in FEV(1) and FVC due to treatment by H(2) receptor blockers may clinically worsen COPD patients who have severe obstruction.