Participants take imatinib capsules once a day for 2 years. If at any time during the study the patient's blood counts begin to rise, disease symptoms develop, or the disease has progressed, the dose of imatinib is increased each week until the disease progression is stopped. Any patient whose disease does not response to treatment after 6 weeks of increased dosing and 30 days at the maximum daily dose of 800 mg is taken off the study and referred for different treatment.