Two cases of lab-confirmed Mycobacterium avium complex infections (MAC) were reported to the New Mexico Department of Health in July 2009. The symptoms, exposures, and presence of MAC were indicative of hot tub lung, a hypersensitivity pneumonitis (HP) - like granulomatous lung disease with non-tuberculous mycobacteria (NTM), that can occur from exposure to hot water aerosols from spas, therapy pools, showers, and indoor swimming pools. Person-to-person transmission does not occur. MAC, a type of NTM, consists of two or more mycobacterial species, M. avium and M. intracellulare. The two cases were employed at a spa establishment with several outdoor tubs. Because of the suspected work-related nature of the illnesses, the cases were referred for investigation to the New Mexico Occupational Health Surveillance Program (NMOHSP), Epidemiology and Response Division (ERD) in February 2010.