Japanese quail (Coturnix coturnix japonica), also called coturnix, is used widely as an experimental bird in avian research. Being small and weighing 100 to 500 g, it requires much less cage space than does the chicken. The coturnix is relatively easy to raise; it appears to thrive on commercially prepared turkey feed (1-3). The coturnix is easy to handle also, and has a large accessible wing vein, resembling the cephalic vein of the chicken, which permits ease of intravenous injection as well as ease of obtaining blood specimens. In our studies of the virulence for fowl of certain mycobacteria isolated from various avian and mammalian species, including man, we had been using chickens which, when full grown, each required cage space at least 10 times that needed for a pair of coturnix. We now have had 3 years of experience with the coturnix in studies on the virulence of Mycobacterium avium. Thirty-six strains have been tested in at least two coturnix each. This report describes the routes of experimental inoculation, the lesions produced, and the results of the tuberculin test.