Flow cytometric analysis of bone marrow aspirates in three cases. The mast cell frequency and phenotype as evaluated by multiparameter flow cytometry. The percentages of CD117++/CD33+ mast cells and of mast cells with aberrant phenotype CD117++/CD33+/CD25+/CD2+ in the three cases are indicated in the graph. In case 1, 0.27% of total bone marrow cells were mast cells. These could be divided, based on expression of CD25 and CD2 in two populations; normal mast cells (pink) (0.16%) and pathological mast cells with expression of CD25 (green) and CD2 (blue) (0.11%). In case 2, total mast cells were 0.09% and the majority of these were CD25+/CD2+ (0.08%). In case 3, the frequency of mast cells was below the detection limit. The antibody combination used was CD2 (FITC; DAKO) - CD25 (PE; DAKO) - CD33 (PerCP-Cy5.5; Becton-Dickinson) - CD34 (PC7; Beckman-Coulter) - CD117 (APC; Beckman-Coulter) – HLA-DR (Pacific Blue; BioLegend) – CD45 (Krome Orange; Beckman-Coulter). 500 000 cells were collected using a Canto2 flow cytometer (BD Bioscience).