The cell walls of mycobacteria resisting all enzymatic and chemical methods for solubilization, good quality DNA require that they are converted into spheroplasts before extraction. Mycobacterium leprae cannot grow in laboratory media, spheroplasts cannot be induced, and therefore the bacteria must be ruptured using physical methods. In these investigations M. leprae was disrupted by sonication. The DNA isolated from sonicated M. smegmatis and sonicated purified DNA isolated from M. smegmatis spheroplasts were used as controls. Additional controls were DNA from E. coli K12 and DNA from armadillo liver. The DNA base compositions determined from melting curves were: armadillo liver, 37.99%; E. coli K12, 51.61%; M. smegmatis spheroplasts, 66.48%; purified sonicated DNA from M. smegmatis, 65.00%; and M. leprae, 66.96%.