The aim of this study was to analyse the efficacy of 2 second mobilization (MB) protocols in 2 groups of patients who failed to obtain enough peripheral blood progenitor cells (PBPC) in the first MB. In 1 group (8 patients), 10 microg/kg of G-CSF was administered, and in the other group (8 patients), a double dosage (10 microg/kg twice a day) was administered. Both groups of patients received Cyclophosphamide (1.5 g/kg) 10 days before the apheresis. No difference was found among both groups of patients in diagnosis, previous chemotherapy, and time elapsed after the first MB. Administration of higher doses of G-CSF decreased the number of apheresis needed in the second MB to complete 2 x 10(6)/kg of CD34+ cells. It also increased the number of patients who achieved sufficient CD34+, namely, 75% versus 50%.