A new liquid cell culture assay for propagating Burkitt lymphoma (BL) cells in the presence of excess allogeneic irradiated bone marrow (BM) has been standardized. The Burkitt cell lines used in this assay were newly established from the tumours of our patients and were either EBV(+) or EBV(-). The phenotypic characteristics of lines were similar to those of the original malignant tumours. With the help of this liquid assay it was possible to evaluate the efficacy of in vitro procedures designed to completely eliminate malignant cells from harvested BM prior to autologous transplantation (i.e., immunomagnetic depletion or antibody-complement-mediated cytolysis). With six out of the seven cell lines tested, the assay permitted the detection of as few as one BL cell in 4 X 10(6) normal BM cells and the measurement of up to 5 log BL cell elimination from 1% contaminated samples.