This study evaluates the relationship between bone marrow growth in a long-term bone marrow culture (LTBMC) system and speed of engraftment of the same marrow following autologous bone marrow transplantation (ABMT). Bone marrow from 21 patients transplanted with unmanipulated, non-cryopreserved autologous marrow was cultured. Samples from 21 normal donors were cultured to establish the normal supernatant cell count range. Supernatant counts from LTBMCs established from marrow taken from patients at the time of bone marrow harvest were compared with the time to neutrophil and platelet engraftment. Supernatant counts, particularly after 1 week in culture, showed close correlation with time to neutrophil and platelet engraftment following ABMT (r = 0.733, p less than 0.01; r = 0.735, p less than 0.01 respectively). Where supernatant cell counts were within the normal range rapid engraftment was predicted (neutrophils greater than 0.5 x 10(9)/l within 21 days, platelets greater than 50 x 10(9)/l within 28 days) and if supernatant counts were below this range, engraftment was predicted to be delayed. After 1 week in culture, the speed of neutrophil and platelet engraftment were correctly predicted in 19 and 18 cases respectively. Preliminary data suggest that LTBMC of marrow obtained 2-6 weeks before harvesting provides similar data, thus allowing the opportunity to intervene, for example with growth factors, in selected patients.