Between July 1994 and December 1996, PBSC were mobilized in 28 patients with poor-risk hematological malignancies and solid tumors. CD34+ cells were positively immunoselected using the Ceprate CS System. By December 1996, 22 patients had been reinfused with a median of 3.325 (0.078-9.5) x 10(6)/kg CD34+ cells. In three patients unselected back-up PBSC had to be transfused along with selected CD34+ cells because of a CD34+ cell number <0.5 x 10(6)/kg. G-CSF (10 microg/kg) was started on day +1 and all patients engrafted within a median day number of 12 (range, 10-22) until leukocytes >1.0 x 10(9)/l and a median day number of 56 (range, 10-180) until platelets >20.0 x 10(9)/l (ie platelet transfusion independence). Time to leukocyte and platelet recovery was significantly shorter in patients receiving >2.0 x 10(6)/kg purified CD34+ cells as compared to patients reinfused with <2.0 x 10(6)/kg CD34+ cells. The hematopoietic recovery time was similar to that of 18 historical control patients treated with unseparated ABMT +/- PBSCT with the exception of a significantly faster leukocyte engraftment in patients receiving >2.0 x 10(6)/kg CD34+ cells and a significantly delayed platelet recovery time in patients receiving <2.0 x 10(6)/kg purified CD34+ cells. There was a trend for a better overall survival and a lower probability of progression/relapse as compared to the historical controls. We observed five episodes of serious opportunistic infections (three pulmonary fungal infections, two cases of cryptosporidiosis) after the take. Four of these patients had been reinfused with <2.0 x 10(6)/kg CD34+ cells probably indicating a delayed immune reconstitution after CD34+-selected PBSCT.