Abstract: The present application discloses rapid Mycobacterium tuberculosis drug susceptibility utilizing real-time PCR of mycobacteriophage D29 DNA. One protocol involves culturing Tb isolates for 48 hours with and without drugs at critical concentrations, followed by incubation with 103 pfu/ml of D29 mycobacteriophage for 24 hours and then real-time PCR. Many drugs can be incubated instantly with Tb and phage. The change in phage DNA real-time PCR cycle threshold (Ct) between control Tb and Tb treated with drugs was calculated and correlated with conventional agar proportion drug susceptibility results. Specifically, 9 susceptible clinical isolates, 22 MDR, and 1 XDR Tb strains were used and Ct control?Ct drug cutoffs of between +0.3 and ?6.0 yielded 422/429 (98%) accurate results for the drugs tested. The Ct values correlated with isolate minimal inhibitory concentration (MIC) for most agents. This D29 qPCR assay offers a rapid, accurate, 1-3 day phenotypic drug susceptibility test.