This study is an open-label, multicenter, Phase I dose-escalation study of the combination of AMN107 and imatinib (STI571) in patients with imatinib-resistant GIST. This study is designed to determine the Phase II dose of AMN107 and imatinib when administered together in patients with imatinib-resistant GIST, and to characterize the safety, tolerability and pharmacokinetic (PK) profile of this combination.