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')2 fragments 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 kappa/lambda ratio, D and D/S(n) values (Kolmogorov-Smirnov statistics) instead of the commonly used kappa/lambda 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 usual FCM method.