Mycobacterium kansasii is a photochromogenic nontuberculous mycobacterium that usually causes infections of the respiratory tract in humans. Although spontaneous resolution of infection has been reported, most patients require antimycobacterial therapy. A three- or four-drug combination--isoniazid, rifampin, and ethambutol and/or streptomycin--usually is prescribed. For evaluation of a new drug, a randomized, double-blind or evaluator-blinded, active-control comparative study design is recommended. Treatment should continue for 18-24 months, and follow-up evaluations should be conducted every 6 months for 3 years. Microbiological outcome is paramount.