Cigarette smoking is thought to adversely affect gastroesophageal reflux. Eight male patients with endoscopic evidence of gastroesophageal reflux had 24-h esophageal pH monitoring while smoking at least 20 cigarettes. This was repeated while abstaining from smoking the following day. In the initial study period, 28.3% of the reflux time occurred within 20 min of smoking a cigarette. There were fewer reflux episodes in the nonsmoking period (95.7 episodes vs 70.0). The patients had significant improvement while in the upright position (57 reflux episodes vs 28.5). Yet, total reflux time was not significantly changed (pH less than 4.0 11.2% of total time smoking vs 10.1% total time nonsmoking). Immediate cessation of smoking decreases the number of daily reflux episodes, but does not significantly affect total esophageal acid exposure in symptomatic patients with endoscopic evidence of gastro-esophageal reflux disease.