Imatinib has become the current standard therapy for patients with chronic myelogenous leukaemia (CML). For a better understanding of the Imatinib-related molecular effects in vivo, we assessed gene expression profiles of Philadelphia Chromosome positive (Ph+) CD34+ cells from peripheral blood of 6 patients with de novo CML in chronic phase. After 7 days of treatment with Imatinib the Ph+ CD34+ cells were reassessed to look for changes in the transcriptome. The expression level of 303 genes was significantly different comparing the transcriptome of the Ph+ CD34+ cells before and after 7 days of Imatinib therapy (183 down-regulated, 120 up-regulated, lower bound 1.2-fold). For a substantial number of genes governing cell cycle and DNA replication, the level of expression significantly decreased (CDC2, RRM2, PCNA, MCM4). On the other hand, therapy with Imatinib was associated with an increase of genes related to adhesive interactions, such as L-selectin or CD44. A group of 8 genes with differential expression levels were confirmed using a gene specific quantitative real-time PCR. Thus, during the first week of treatment, Imatinib is preferentially counteracting the bcr-abl induced effects related to a disturbed cell cycle and defective adhesion of leukemic Ph+ CD34+ cells.