Susceptibility of five poplar clones to bark cancer (Dothichiza populea Sacc. et Br) was studied from June 2001 until May 2002. Examinations were carried out by artificial inoculation with mycelium of three isolates of D. populea at the end of each month. Greater susceptibility to the fungus based on percent of infections and length of necrosis were expressed by clones I-214 and B-229 in relation to clones Pannonia, B-81 and 182/81. Based on the same parameters were determined differences in agressivity of isolates from clones B-229, I-214Bč and 1004. Separately, the same method of inoculation was applied on cuttings of cl. I-214 on which were testing of patogenicity of nine isolates of D. populea in conditions of greenhouse in April 2002. It was found out that there were significant differences between isolates relating to the expressed patogenicity.