Background: Peripheral blood progenitor cells (PBPC) can be collected by most blood cell separators. The present study was designed to compare two new techniques for PBPC collection. Design: Prospective, randomized study. Setting: Haemapheresis Unit and Haematological Division of a University Clinic. Patients: 20 patients with non-Hodgkin’s lymphoma, Hodgkin’s disease and thyroid cancer. Material and Methods: 20 patients with malignancies underwent PBPC collection with a ‘reduced-volume’ programme (Fresenius AS 104) and a single-needle technique (Haemone-tics MCS 3p), respectively. PBPC were mobilized by combined chemotherapy and cytokine administration or application of growth factor alone. Blood counts, CD 34 expressing cells and mononuclear cells (MNC) were determined before apheresis and in the PBPC product. Granulocyte macrophage colony-forming units (CFU-GM) were determined in the apheresis product. PBPC were frozen at controlled rates and stored in liquid nitrogen until they were used for autologous transplantation after high-dose chemotherapy. Results: 32 PBPC collections were carried out with the Fresenius AS 104 and 27 separations with the Haemonetics MCS 3p device. Median product volume was 106 ml using the Fresenius AS 104 apparatus and 156 ml in the case of the Haemonetics MCS 3p machine. The median CD 34-expressing cell count was 1.0×106/kg body weight for the Fresenius device and 0.6 ×106 for the Haemonetics cell separator. The cell recoveries of the two studied devices were significantly different. Six patients were grafted after high-dose chemotherapy. Five showed signs of haematopoietic recovery after autologous PBPC retrans-fusion. Conclusions: The study reported here revealed that PBPC could be collected by both techniques. Although the collected amounts of CD34 expressing cells were similar, cell recoveries were significantly higher in the Haemonetics machine. Using the ‘reduced-volume’ procedure no additional centrifugation prior to cryopreservation was necessary to remove the plasma from the apheresis product. Haematopoietic engraftment was achieved after retransf