Abstract:Flow cytometry (FCM) has gained wide use in the determination of clonality in B‐cell lymphoproliferative diseases and many methodological variations exist. We have compared the suitability of a) dual fluorochrome (FITC/PE)‐labelled monoclonal antibodies, b) single fluorochrome (FITC)‐labelled monoclonal antibodies and c) F(ab')2fragments of FITC‐labelled polyclonal antibodies for flow cytometric determination of clonality using commercially available software and a short sample preparation protocol. The FCM method was validated by analysis of immunoglobulin heavy chain and light chain gene rearrangements. We recommend the use of FITC‐labelled monoclonals to obtain three parameters, the k/λ ratio, D and D/S(n) values (Kolmogorov‐Smirnov statistics) instead of the commonly used k/λ ratio and D values only. This allows the use of a rapid sample preparation protocol to blood and bone marrow aspirates without sacrificing sensitivity or specificity obtained by the usu