The use of a combination of G-CSF and GM-CSF versus G-CSF alone, after cyclophosphamide (4 g/m2) was compared in two randomized phase III studies, including 120 patients. In study A, 60 patients received 5 x 2 microg/kg/day of G-CSF and GM-CSF compared to 5 mug/kg/day of G-CSF. In study B, 60 patients received 2.5 x 2 microg/kg/day G-CSF and GM-CSF compared to G-CSF alone (5 microg/kg/day). With the aim to collect at least 5 x 10(6)/kg CD34 cells in a maximum of three large volume leukapherises (LK), 123 LK were performed in study A, showing a significantly higher number of patients reaching 10 x 10(6)/kg CD34 cells (21/29 in G+GM-CSF arm vs 11/27 in G-CSF arm, P=0.00006). In study B, 109 LK were performed, with similar results (10/27 vs 15/26, P=0.003). In both the study, the total harvest of CD34 cells/kg was twofold higher in G-CSF plus GM-CSF group (18.3 x 10(6) in study A and 15.85 x 10(6) in study B) than in G-CSF group (9 x 10(6) in study A and 8.1 x 10(6) in study B), a significant difference only seen in multiple myeloma, with no significant difference in terms of mobilized myeloma cells between G-CSF and GM-CSF groups.