To determine if reducing the intensity of the mobilizing chemotherapy protocol used would alter the number and/or quality of the progenitors mobilized in patients with chronic myelogenous leukaemia (CML), we undertook a pilot study. 36 consecutive CML patients previously treated only with hydroxyurea were given mobilization therapy within 12 months of diagnosis. 17 patients were treated by the ICE protocol and 19 patients received the mini-ICE protocol. The leukapheresis product collected from 22/36 patients (62%) was entirely Ph-negative. The cytogenetic results between ICE and mini-ICE-treated protocols were not significant, although the reduction in median days of hospitalization required for the mini-ICE versus the ICE protocol was highly significant (P < 0.0001). There was no significant difference in the yield of CD34+ cells and CFU-GM collected. No patient in the mini-ICE protocol experienced high-grade oral mucositis and GI toxicity whereas three such cases occurred with the ICE protocol. No patient died of the mobilization procedure in either group.