Frequency of resistant colonies emerging in the presence of imatinib is higher than with PD166326. Single colonies of Ba/F3 cells growing in the presence of inhibitor were picked and analyzed. Shown is the incidence of resistant colonies that grew up in relation to the number of Ba/F3-Bcr-Abl wild-type (Ba/F3-BA-wt) cells in liquid culture in the presence of imatinib (A) or PD166326 (B), or in solid culture conditions in the presence of imatinib (C). Resistant colonies are itemized according to wild-type (wt; ▪) or mutant (mut; □) sequence of Bcr-Abl.