A two-stage long-term bone marrow culture (LTBMC) has been used to assess haemopoietic supporting ability from patients following allogeneic bone marrow transplantation (BMT). Irradiated confluent LTBMCs derived from recipients following BMT were recharged with flow cytometry sorted CD34+/CD38- cells from normal BM donors. The output of granulocyte/macrophage colony-forming cells (GM-CFC) in the non-adherent fraction of the cultures was monitored weekly until output ceased. Patient stromal cell function was determined by comparing the percentage of the total cumulative GM-CFC output to the output from normal control stroma. Neutrophil recovery was rapid and complete early in the post-transplant period. However, in contrast, GM-CFC recovery was significantly reduced in all patients up to 5 years after BMT. In 58% of patients studied following BMT the BM stroma is considerably compromised in its ability to support early uncommitted haemopoietic cells contained within the CD34+/CD38- cell fraction of normal BM. Bone marrow stroma from BMT recipients exhibited severe deficits in their abilities to support primitive haemopoietic cells and in some patients this effect lasted for several years. While the growth of stroma from patients following BMT was severely delayed and often incomplete, characterisation of cells types using APAAP techniques did not show significant differences in proportion when compared with normal cultures.(ABSTRACT TRUNCATED AT 250 WORDS)