A process for detecting, by flow cytometry, the presence of normal plasma cells and of tumoral plasma cells in a sample of cells from a patient, said process comprising the following steps: a) bringing said sample of cells into contact with: - a κ chain marker, a λ chain marker, and a marker selected from: a CD38 marker and a CD138 marker, each of the three markers emitting a different signal (hereinafter the 'first three signals'), and - one or more tumoral plasma cell marker(s), each of these one or more marker (s) emitting a single signal otherwise known as the 'single detectable signal' (hereinafter the 'fourth signal'), different than said first three signals, and - one or more normal plasma cell CD marker (s), each of these one or more marker(s) emitting a single signal otherwise known as the 'single detectable signal' (hereinafter the 'fifth signal'), different than the first four signals, b) detecting the plasma cells characterized by: - a positive signal with a CD38 marker or a CD138 marker, and - a positive signal with a κ chain marker or a λ chain marker, c) detecting the tumoral plasma cells among the plasma cells detected in step b) having at least one of the following criteria: - a positive signal with at least one marker specific for tumoral plasma cells, and/or - a negative or significantly reduced signal with at least one marker for normal plasma cells, d) analyzing the results obtained during steps b) and c) and determining the presence of normal plasma cells and of tumoral plasma cells. a) bringing said sample of cells into contact with: - a κ chain marker, a λ chain marker, and a marker selected from: a CD38 marker and a CD138 marker, each of the three markers emitting a different signal (hereinafter the 'first three signals'), and - one or more tumoral plasma cell marker(s), each of these one or more marker (s) emitting a single signal otherwise known as the 'single detectable signal' (hereinafter the 'fourth signal'), different than said first three signals, and - one or more normal plasma cell CD marker (s), each of these one or more marker(s) emitting a single signal otherwise known as the 'single detectable signal' (hereinafter the 'fifth signal'), different than the first four signals, - a κ chain marker, a λ chain marker, and a marker selected from: a CD38 marker and a CD138 marker, each of the three markers emitting a different signal (hereinafter the 'first three signals'), and - one or more tumoral plasma cell marker(s), each of these one or more marker (s) emitting a single signal otherwise known as the 'single detectable signal' (hereinafter the 'fourth signal'), different than said first three signals, and - one or more normal plasma cell CD marker (s), each of these one or more marker(s) emitting a single signal otherwise known as the 'single detectable signal' (hereinafter the 'fifth signal'), different than the first four signals, b) detecting the plasma cells characterized by: - a positive signal with a CD38 marker or a CD138 marker, and - a positive signal with a κ chain marker or a λ chain marker, - a positive signal with a CD38 marker or a CD138 marker, and - a positive signal with a κ chain marker or a λ chain marker, c) detecting the tumoral plasma cells among the plasma cells detected in step b) having at least one of the following criteria: - a positive signal with at least one marker specific for tumoral plasma cells, and/or - a negative or significantly reduced signal with at least one marker for normal plasma cells, - a positive signal with at least one marker specific for tumoral plasma cells, and/or - a negative or significantly reduced signal with at least one marker for normal plasma cells, d) analyzing the results obtained during steps b) and c) and determining the presence of normal plasma cells and of tumoral plasma cells.