The ability of the MGITTM system to grow and detect the growth of Mycobacterium paratuberculosis was tested under a variety of conditions, including the addition of mycobactin J, egg yolk emulsion and antibiotic mixtures. One-half McFarland suspensions were prepared from ATCC 19851 and ATCC 19698 grown on 7H10 plates supplemented with mycobactin J. Multiple dilutions were prepared from the suspensions and used to inoculate sets of MGIT tubes at the standard pH of 6.6 or tubes adjusted to 5.7. One-half milliliter of MGITTM OADC was added to each tube, supplements were added, alone or in combination, the tubes were incubated at 37°C and read daily using a 365 nm transilluminator. Tubes containing 1 ml of egg yolk emulsion turned out to be unsuitable. The emulsion apparently was a good enough reducing agent to interfere with the oxygen sensor on the bottom of the tubes and the emulsion also separated out in many cases. Tubes supplemented with mycobactin J grew and fluoresced to indicate that growth had occurred. The time to detection was about the same at pH 6.6 or 5.7. MGIT tubes without mycobactin J or other supplements did not support the growth of either ATCC strains at pH 6.6. However, MGIT tubes adjusted to pH 5.7 supported the growth of both strains without supplements.