Abstract:In order to characterize the effect of T lymphocytes on thein vitrogrowth of erythroid progenitor cells (EPC), we have optimized an assay for evaluating the influence of autologous T‐ lymphocyte clones on BFU‐e, grown from PBMNCs depleted of T lymphocytes. Testing a large number of T‐lymphocyte clones from 2 individuals we found that, irrespective of immunological phenotype, all clones tested were found to enhance the growth of BFU‐e. Thus, no evidence for a functional dichotomy between CD4+ and CD8+ T lymphocytes was found in this system. The enhancing effect worked across a histocompatibility barrier and was, at least in part, mediated by soluble factors. We therefore conclude that the role of the majority of cloned normal T lymphocytes in the regulation of thein vitrogrowth of EPC is a support