With the aim of facilitating the ex vivo manipulation of peripheral blood hematopoietic progenitors (CPCs = circulating progenitor cells) collected by leukapheresis, we removed polymorphonuclear cells and monocytes that naturally adhere to nylon wool fibers. Leukapheresed cells harvested at the time of hematopoietic recovery after cancer therapy with high-dose cyclophosphamide plus hematopoietic growth factors were incubated with nylon wool fibers for 1 h at 37 degrees C. Evaluation of the cells non-adherent to the nylon wool in all experiments (n = 14) showed that the median recovery of nucleated cells and CPCs detected as CD34+ cells, CFU-GM and BFU-E was 16.4% (range 4.8%-34.0%), 60.0% (range 30.8-80.8%), 60.9% (range 33.4-74.5%) and 65.5% (range 30.8-69.2%), respectively. Therefore exposure to the nylon wool determined a selective removal of mature cells and a complementary enrichment of CPCs. The wide range of results depended on the significantly different cell compositions of the unmanipulated leukaphereses. The latter from patients receiving rhG-CSF (n = 10) comprised a median of 88.5% (range 77.8-93.8%) and 11.5% (range 6.2-22.2%) polymorphonuclear and mononuclear cells, respectively. In contrast, leukaphereses from patients receiving rhGM-CSF or PIXY321 (n = 4) comprised a median of 71.1% (range 55.4-85.0%) and 28.9% (range 15.0-44.6%) polymorphonuclear and mononuclear cells, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)