The effect of nifedipine administration (10 mg) on esophageal acid exposure time was investigated in 11 non-reflux esophagitis (non-RE) patients and 11 grade C (Los Angeles classification) reflux esophagitis (RE) patients. In each subject, esophageal pH monitoring was performed, with the subject in the supine position, preprandially (1 h) and 3-h postprandially after oral administration of a placebo in the morning and oral administration of nifedipine (10 mg) in the afternoon on the same day. In the non-RE patients, there was no difference in the esophageal acid exposure time between administration of the placebo and that of nifedipine. In patients with RE, the esophageal acid exposure time after the administration of nifedipine was significantly (P<0.05) longer than that after the placebo. In patients with severe RE, the severity of RE may worsen with nifedipine administration.