The advent of new therapeutic approaches to multiple myeloma made necessary the introduction of novel methods for detection of minimal residual disease. Among others approaches residual disease can be detected by the immunofluorescence using flow cytometry. We have examined the co-expression of CD19, CD38, CD45, CD54, CD56, and CD138 molecules in cells of peripheral blood and bone marrow aspirates in patients with multiple myeloma by 3-color flow cytometry. For the detection and characterization of multiple myeloma cells, combinations of following antibodies were used: anti-CD19 FITC, anti-CD38 FITC, anti-CD38 PE, anti-CD54 FITC, anti-CD56 PE-Cy5, anti-CD45 PE, anti-CD45 PE-Cy5 (Immunotech) and anti CD138 PE (Serotec). The samples were analyzed using EPICS XL (Coulter) flow cytometer, and the analysis was based on at least 10,000 events. Samples from 17 patients were analyzed. The percentage of multiple myeloma cells ranged between 0.3% and 54.2% in bone marrow aspirates and between 0.0 and 11.8% in periferal blood. The expression of CD138, CD38, CD54 and CD56 molecules was found in 100%, 100%, 85% and 68% of examined cases, respectively. In our opinion, multiple myeloma cells are best characterized by following combinations of antibodies: CD38 FITC/CD138 PE/CD45 PE-Cy5, CD54 FITC/CD138 PE/CD56 PE-Cy5 or CD54 FITC/CD38 PE/CD 56 PE-Cy5. The identification of a malignant clone is the first and the most important step in the characterization of the disease, determination of its prognosis and the detection of residual disease after treatment. Three-color flow cytometry represents a method which can meet these goals.