The mobilisation characteristics of ifosfamide and etoposide followed by Granulocyte Colony-Stimulating Factor fGCSF, filgrastim) were analysed in 17 patients with malignant lymphoma and 24 patients with solid tumours, with respect to the optimum time to harvest progenitor cells and to the yields of progenitor cells that could be achieved. In addition, we analysed patient characteristics which could influence the size of the progenitor cell harvest. Clinical parameters which were co-related with the size of the circulating progenitor cells (CPC) harvests were: the dose of G-CSF, dose of if osfamide, sex, age, diagnosis and extent of pretreatment. CPC were mobilised with 3 g/m2 (n = 11) or 4 g/m2 (n = 30) ifosfamide on day 1 and etoposide 100 mg/m2/day, on days 1-3 i.v., followed by daily s.c. injections with filgrastim 5 micrograms/kg (n = 26) or 10 micrograms/kg (n = 15) from day 4. The maximal progenitor cell harvest was achieved on either day 12 or day 13 after the start of the ifosfamide/etoposide course. The median number of leukaphereses necessary to harvest the target quantity of 3 x 10(6) CD34+ cells/kg body weight was 1 (range 1-9). Thirteen/41 (32%) of the patients did not achieve the target yield of 3 x 10(6) CD34+ cells/kg. By multivariate analysis, the dose of GCSF and prior irradiation were associated with the number of progenitor cells harvested, while all other parameters, induding the dose of if osfamide and number of previous chemotherapy courses, were not. Sixteen patients received two or more mobilisation courses. Despite the fact that the same mobilisation schedule was used, the progenitor cell yields after the first mobilisation course did not predict the results after the subsequent mobilisation courses, indicating that unknown transient factors may significantly influence the CPC yield.