Clarithromycin resistance in Helicobacter pylori has increased the incidence of eradication failure. Clarithromycin is a key drug in the current treatment regimens for H. pylori infection, and it is also used for nontuberculous mycobacteriosis (NTM). The rate of H. pylori infection in 15 patients with NTM who were on longterm clarithromycin, rifampicin, and other drug therapy wasexamined, using the [13C] urea breath test. H. pylori was detected in 5 of the 15 patients (33.3%), whichwas significantly lower than the prevalence of H. pyloriin subjects who had routine upper gastrointestinal endoscopy in Japan (P = 0.0006). Thus, H. pylori resistance to clarithromycin is suggested to be low in patients with longterm administration, and the possibility exists of a combination of clarithromycin and rifampicin as a second-line therapy for the eradiation of H. pylori.