The lytic potency of a newly isolated phage Al-1 obtained from the laboratory strain M. leprae murium "Douglas" was examined. The phage was multiplied on the laboratory strain M. smegmatis ATCC 607 and for the lytic test 0.1 ml of suspension containing PFU 10(5) was used. In the whole 18 mycobacterial strains both slowly and fast growing multiplied in liquid Sula's medium were tested. For phage lytic tests two simple agar media and standard Redmond's medium RVA-24 were used. The examined slowly growing mycobacteria (H37Rv. M. bovis "Ravenel", M. avium "Kirchberg", M. kansasii "Svizenský", M. tbc INH resist., M. tbc INH, STM, PAS resist.) were resistant to the tested phage similarly as M. phlei from the group of fast growing strains. The results of phage tests on all three used media were characterized by a confluent phage lysis with the exception of the strain M. butyricum "Rabinovic", in which even on a very rich media an incomplete lysis with countable plaques was found out. The use of the phage Al-1 for the phage typification also of the strain M. leprae murium is considered on the basis of the inhibition growth tests on Ogawa's egg media.