Cultivation of Mycobacterium lepraemurium in cell-free media has not yet been successful, perhaps because of deterioration of the nutritional quality of the medium with prolonged incubation at 37 degrees C. Trials with a continuous culture technique, involving regular change of a simple liquid medium prepared from human placenta, demonstrated active fission of the Myco. lepraemurium cells. Abundant growth in the form by macroscopically visible colonies has not been achieved even after prolonged incubation up to 8 months.