Mycobacteria are responsible for a number of important human and animal infections. One particular problem posed by these organisms when using molecular methods is the physical strength of the cell wall, so that sensitivity of detection is limited by the efficiency of DNA extraction. Over the last 15 years we have been exploiting a broad host range, lytic phage (D29) as a DNA lysing agent to develop rapid and sensitive tests to detect and identify mycobacterial pathogens. In addition to being very efficient at lysing mycobacteria, phage have another advantage over chemical extraction methods in that only viable cells are lysed, and therefore successful lysis using phage also reports on the viability of the cell detected. We have now developed a method that can successfully detect mycobacteria within 6 h, and have applied this to a number of different samples. During these studies we have discovered new features of the phage-host interaction that has allowed us to better understand and improve our test methods. Most recently we have used the method to show that viable M. bovis is present in the blood of skin-test positive cattle, despite the fact that the dogma of the disease suggests it should not be present. In addition we are now using this method to improve detection and control of bovine TB in naturally infected herds in the UK. The method developed is simple and can be applied to detect any mycobacteria in a range of different sample types, opening up the possibility of an enhanced understanding of these difficult to grow bacteria.