Cover photograph (Copyright © 2006, American Society for Microbiology. All Rights Reserved.): Molecular protocols offer a rapid alternative to the more labor-intensive growth, phenotypic, and biochemical tests classically used to identify Mycobacterium isolates to the species level. Shown is a composite of individual colonies of M. tuberculosis (strain ATCC 25794, center), M. smegmatis (strain mc² 155, top left), M. avium subsp. avium (strain ATCC 19074, top right), and M. avium subsp. hominisuis (clinical isolate MAC001, replicated center right to bottom left). Images were taken at ×400 microscopic magnification following culture on 7H11 agar for 1 month, 1 week, 2 weeks, and 2 weeks of growth, respectively, in a 35°C incubator with 5% CO2. Colony images were digitally extracted from the background of the original photographs and were resized to give the composite shown. (Image produced by Richard C. Huard and Dave A. Theys.) (See related article on page 4271.)