Using B1, Y29/55 and AL2 monoclonal antibodies (MoAbs) to target Burkitt lymphoma (BL) cell lines, we defined optimal conditions to lyse, in the presence of baby rabbit complement, BL cells in excess bone marrow (BM). After the purging procedure, down to one residual BL cell in 10(6) normal ones was detectable with a liquid cell culture assay. Using a cocktail of three MoAbs, on five different cell lines were observed more than 4 log BL cell depletion in samples contaminated with 1% BL cells and only one failure of the procedure on 17 experiments. However, a sixth line was constantly resistant to the procedure.