Abstract Bone marrow cells from 109 patients (median age 60) with newly diagnosed acute myeloid leukaemia (AML) were prospectively immunophenotyped (IP) and the prognostic value of monoclonal antibody (MAB) reactivities was analysed to detect differences in complete remission rates and survival, not only between groups of MAB + and − bone marrow cells, but also in cases with or without prominent MAB reactivity as compared to normal BM reactivity of the respective MABs. This approach was based on the assumption that the qualitative expression of antigens is not an all or none phenomenon, but that different degrees of expression of antigens exist. Patients with significantly elevated CD13 (MY7+) cells in bone marrows (CD13 > reference value + one standard deviation) (S.D.) showed decreased probability of entering CR ( p < 0.05) and a significantly shorter survival ( p < 0.05). Superior CR rates ( p < 0.05) without difference in long-term survival were seen in patients with low CD33 (MY9) or low HLA-DR expression, while high CD14 (MY4) expression showed a trend towards an adverse factor ( p = 0.12). No other antibody reactivities showed differences in CR rates (CD3, CD20, CDw65 (VIM-2) and NAT-9). The more prominent bone marrow expression of CD33 antigen than CD13 (CD33/CD13 > 1) correlated to a better chance of entering CR ( p = 0.01) and to improved survival ( p = 0.002), while the expression of high numbers of VIM-2+ cells was a favourable prognostic factor regarding length of survival ( p = 0.002). The importance of a high CD33/CD13 ratio as a positive prognostic factor was evaluated using stratified analysis according to age or leucocyte counts at presentation. In both cases, CD33/CD13 was associated with longer survival (age: p = 0.05, leucocyte counts: p = 0.03). A Cox multiparameter analysis revealed that the CD33/CD13 ratio was a favourable prognostic factor ( p = 0.03) together with age ( p = 0.001) and leucocyte counts in peripheral blood ( p < 0.01). We conclude that establishing the immunologic phenotype can be of prognostic value in cases of AML, especially with regard to the relationship between the CD33 and CD13 antigens.