We have previously reported that mobilization of Philadelphia (Ph) chromosome-negative progenitors is possible in a significant number of Ph1-positive acute lymphoblastic leukaemia (ALL) and chronic myelogenous leukaemia (CML) patients. In this pilot study we employed the same approach for patients with RAEB-t, secondary AML (sAML) and therapy-related AML (t-AML). All patients except one had double or complex cytogenetic abnormalities in marrow cells before mobilization therapy. All patients received an idarubicin-containing regimen (mini-ICE protocol) followed by rh-G-CSF and the first leukapheresis was performed as they were recovering from aplasia. In six out of nine patients the leukapheresis product was entirely karyotypically normal, combined with a significant number of CFU-GM. CD34+ cells and LTC-IC. Recovery time from mobilization therapy was short and no patient died as a result of the procedure. To date, three patients have undergone autografting using their karyotypically normal collections, of which two (sAML) are alive with karyotypically normal marrow a few months after autografting.