The Runyon classification of nontuberculous mycobacteria based on the rate of growth, production of yellow pigment and whether this pigment was produced in the dark or only after exposure to light. On these bases, the nontuberculous mycobacteria are divided into four groups:

1. Runyon I (Photochromogens): slow growing, and produce a yellow-orange pigment when exposed to light. M. kansasii, M. marinum

2. Runyon II (Scotochromogens): slow growing, and produce a yellow-orange pigment in light or in the dark. M. scrofulaceum, M. gordonae, M. szulgai

3. Runyon III (Nonchromogenic): slow growing, and do not produce pigment. M. avium-intracellulare, M. xenopi, M. terrae

4. Runyon IV (Rapid Growers Runyon): rapid growing (colonies in 5 days). They do not produce pigment. M. fortuitum, M. peregrinum, M. abscessus, M. chelonae