This work was performed with L 428, a cell line established in 1978 from a patient with Hodgkin's disease. These in vitro cells represent counterparts of in vivo Hodgkin and Sternberg-Reed cells. L 428 and its derived sublines produce a significant amount of colony-stimulating factor (CSF) compared to standard preparations of CSF (fetal liver conditioned medium). Hodgkin-cell-derived conditioned medium, tested in cord-blood assays and in semi-solid agar systems, induced myeloproliferation predominantly. Production of CSF is independent of fetal calf serum concentration in the cultures. L 428-conditioned medium could provide an excellent source for characterization and purification of granulocyte CSF.