The effect of peripheral blood T lymphocytes from 42 patients with advanced Hodgkin's disease (grade III and IV) on the autologous marrow erythroid colony formation was studied in diffusion chamber culture. It was found, that unfractionated T lymphocytes suppress the BFU-E--(burst forming unit erythroid) and CFU-E--(colony forming unit erythroid)--derived colony formation by releasing an inhibitory activity. The suppression of colony formation was noted already at 0.25 x 10(5) cell concentration. In experiments with 0.5 x 10(5) and 1.0 x 10(5) T cells the inhibitory effect was increased. Subsequently it was shown, that this inhibition was generated by radioresistant, CD8+ and HLA-DR- subset of T cells. In control experiments, T lymphocytes from healthy subjects had no influence on the erythroid colony formation.