Expansion of cord blood (CB) haemopoietic cells has been investigated with the aim of reducing cytopenia following transplantation. We investigated the increase in total nucleated cells, colony-forming cells (CFC), CD34+ cells and long-term culture-initiating cells (LTC-IC) by limiting dilution after a 14-day culture of CB CD34+ cells (5 x 10(3)/ml) with SCF, IL-3, IL-6, GM-CSF and G-CSF all at 10 ng/ml. On average nucleated cells increased 2500-fold, CD34+ cells 39-fold and CFU-GM 49-fold with maintenance of BFU-E. The more primitive LTC-IC expanded on average 2.5-fold. Expansion of a 20% aliquot of a CB donation could provide a 5-7-fold increase in progenitor cells, and a 1570-fold increase in post-progenitor cells compared to an untreated donation.