Laboratory diagnosis of mycobacterial infection is complicated by the fastidious growth requirements of the bacillus organism. Delays in diagnosis can impede effective treatment and surveillance of the disease. Control of Mycobacterium tuberculosis has also been aggravated by the emergence of multidrug-resistant tuberculosis, and enhanced methods of antibiotic susceptibility testing are needed. Molecular laboratory techniques and advances in rapid culture methods have led to the development of diagnostic and drug susceptibility tests that are rapid and reliable. This article describes recent innovations in the molecular diagnosis and antibiotic susceptibility testing of M tuberculosis.