A 49-year-old woman presented with exertional dyspnea. Chest CT revealed patchy areas of ground-glass attenuation and ill-defined centrilobular nodules scattered in both lungs. Bronchoalveolar lavage (BAL) fluid showed lymphocytosis. Transbronchial lung biopsy revealed bronchiolocentric alveolitis and well-formed non-necrotizing granulomas were present. She had used a jet bath before the onset of symptoms and mycobacterial culture revealed the presence of Mycobacterium avium complex (MAC) in sputum sample, BAL samples and jet bath water. Restriction fragment length polymorphism (RFLP) analysis revealed that the isolated MAC were essentially clonal. She had used the jet bath for the inhalation provocation study, and after the challenge she complained of dyspnea and have body temperature increased. We diagnosed hot tub lung due to Mycobacterium avium complex. Because avoidance of the jet bath caused improvement of her symptoms and reduced her fever and PaO2 increased by 10 Torr but did not improve the CT findings, antimycobacterial drugs were prescribed. The patient recovered fully. This case proves that the cause of hot tub lung is the use of jet bath through the inhalation provocation study.