Runyon classification system /run″yən/ [Ernest Runyon, 20th-century American microbiologist] , a system of identifying mycobacteria on the basis of pigmentation and growth condition of the organisms. It includes group I, yellow-pigment photochromogens; group II, yellow-to-orange-to-red–pigment scotochromogens; group III, white-to-tan nonphotochromogens; and group IV, rapid-growing saprophytes.
