Current therapy for pulmonary tuberculosis involves 6 months of treatment with isoniazid, pyrazinamide, rifampin, and ethambutol or streptomycin for reliable treatment efficacy. The long treatment period increases the probability of noncompliance, leading to the generation of multidrug-resistant isolates of Mycobacterium tuberculosis. A treatment option that significantly shortened the course of therapy, or a new class of antibacterial effective against drug-resistant M. tuberculosis would be of value. ABT-255 is a novel 2-pyridone antibacterial agent which demonstrates in vitro potency and in vivo efficacy against drug-susceptible and drug-resistant M. tuberculosis strains. By the Alamar blue reduction technique, the MIC of ABT-255 against susceptible strains of M. tuberculosis ranged from 0.016 to 0.031 µg/ml. The MIC of ABT-255 against rifampin- or ethambutol-resistant M. tuberculosis isolates was 0.031 µg/ml. In a murine model of pulmonary tuberculosis, 4 weeks of oral ABT-255 therapy produced a 2- to 5-log₁₀ reduction in viable drug-susceptible M. tuberculosis counts from lung tissue. Against drug-resistant strains of M. tuberculosis, ABT-255 produced a 2- to 3-log₁₀ reduction in viable bacterial counts from lung tissue. ABT-255 is a promising new antibacterial agent with activity against M. tuberculosis.