We have previously reported that the rate of haematopoietic recovery following Autologous Blood Stem Cell Transplantation (ABSCT) could be influenced by the type of conditioning regimen or by the underlying disease. Furthermore, Peripheral Blood Stem Cell (PBSC) growth was found to be sensitive to stimulation by irradiated allogeneic stromal layers. In the present study, we used the long term culture system (LTC) to investigate the quality of the bone marrow (BM) microenvironment from patients who had undergone ABSCT for either Malignant Lymphoma (ML, 13 patients) or Multiple Myeloma (MM, 8 patients) after conditioning regimens comporting myeloablative chemotherapy (CT) or Total Body Irradiation (TBI). Among the 13 ML patients, 10 received CT conditioning and 9 of the 10 BM samples developed a complete confluent stromal layer. The remaining 3 ML patients received TBI prior to ABSCT and 2 of the 3 samples developed confluent stroma. In contrast, when LTC were established with BM from the 8 MM patients, all of whom were treated with TBI prior to ABSCT, only 3 of the 8 marrow samples developed a complete confluent stromal layer. Thus BM from patients who had received CT conditioning therapy tended to form confluent stroma more often than BM from those who had received TBI (p = 0.08). CFU-GM production was also evaluated for the stromal layers derived from all transplanted patients.(ABSTRACT TRUNCATED AT 250 WORDS)