A minimum of 100 patients who are interferon refractory will receive STI571 administered at a dose of 400 mg once a day. In addition, the protocol is also open for patients who are intolerant to interferon-alpha in order to get a preliminary evaluation of their response to STI571 therapy. Up to 100 intolerant patients will be enrolled. Enrollment of intolerant patients will cease at 100, or whenever the 100 refractory patients are accrued, whichever comes first.