Five strains of rapidly growing scotochromogenic mycobacteria have been isolated from soil and sputum. This study comprises 101 biological, biochemical and morphological characteristics, as well as the behaviour against the common antituberculous drugs at several concentrations. The organisms are considered to belong to a new species of the genus Mycobacterium bacterium and are named Mycobacterium valentiae sp. nov. They have been deposited in the American Type Culture Collection, Rockville, Md., U.S.A. as 29356 and the Czechoslovak Collection of Microorganisms in the Czechoslovak National Collection of Type Cultures, Institute of Epidemiology and Hygiene Prague, as My 220/77.