The prognostic value of cell differentiation antigens detected with the monoclonal antibodies of VI series was studied in 242 cases of acute nonlymphoblastic leukemia (ANLL) treated in 7 cooperating centers. A significantly higher complete remission rate was observed in patients with a higher expression of CD-15 antigen detected by VIM-D5 antibody than in those with lower values. These significant differences were proved when comparing subgroups with VIM-D5 positivity of blastic cells < 15 and > 15% (p < 0.01) as well as in the subgroups with values < 50% (median value) and ≥ 50% (p < 0.02). Our studies suggest the VIM-D5 positivity of ANLL cells to be favourable prognostic factor predicting the ability to achieve complete remission. Further studies are needed to establish whether the expression of the VIM-D5-defined antigen may serve as a prognostic factor related to survival.