ABSTRACT Mycobacterium triplex , a recently described slowly growing nontuberculous mycobacterium, was isolated from a Finnish patient with pulmonary mycobacteriosis. The disease was successfully treated with antimycobacterial drugs. The strain isolated, which was similar to the type strain but differed slightly from the species description, was regarded as a variant of M. triplex sensu stricto. According to present knowledge this variant of the species has never been isolated before.