Performing antimicrobial susceptibility tests on intestinal isolates of M. paratuberculosis and M. avium has been somewhat problematic due to a number of factors including, relatively slow growth, intracellular survival, cidal versus static activity and resistance to many anti-infective agents. While the commercial radiometric broth technique has proved to be a valuable approach to determining susceptibility of human mycobacterial isolates, current endpoint determination does not take into account a number of important kinetic parameters and does not necessarily provide information on cidal activity. We examined the effects of selected antimycobacterial agents including monensin (ionophore), ethambutol, rifabutin and ciprofloxacin, alone and in combination with one of several cytokines, interferon, tumor necrosis factor and GM-CSF on growth of enteric mycobacterial isolates. Extracellular and intracellular susceptibility were performed in microwells containing Middlebrook broth only or macrophage cells in culture respectively. At selected time points following incubation, aliquots from the wells were inoculated into radiometric vials for determination of static or cidal activity. A lysing agent was added to wells of infected macrophages prior to inoculation. Susceptibility was determined using established procedures which compare treated groups to a 1% survival population of the inoculum. We conclude that additional and valuable information including kinetics, combinatorial effects and cidal or static activity can be obtained and is essential in evaluating the antimycobacterial capabilities of potential therapeutic regimens. While certain antimicrobial agents proved effective either alone or in combination in inhibiting growth of extracellular mycobacteria, these same treatments were not able to inhibit intracellular mycobacteria in a similar manner and the effects were mostly static resulting in regrowth when drugs were removed. Addition of cytokine treatment in select cases resulted in cidal activity.