 This is an open-label, phase II study of PTK787ZK222584 designed to determine the safety and efficacy of PTK787ZK222584 in the treatment of imatinib-resistant GIST. The PTK787ZK222584 dose used is 1250 mg daily. Six patients will first enter the study using a two-stage approach. If clinical benefit is obtained in 1 of 6 patients, 9 and 30 additional patients will be entered into the protocol a maximum total number of 45 patients will be entered. Clinical benefit is defined as the occurrence of one or more of the following 3 measures: 1 objective response to PTK787 a confirmed or unconfirmed partial response PR or a complete response CR; 2 metabolic response defined as 50 decrease in the standardized uptake value SUV of FDG uptake in 1 FDG-avid lesions in one or more of the patients; or 3 stabilized disease for 3 months or longer accompanied by symptomatic or performance status improvement. Medical history, current medical conditions, weight, height, and an electrocardiogram are recorded prior to the study entry. Other baseline examinations include a chest X-ray, hematologic tests, a coagulation panel, serum chemistries, urine analysis, a serum pregnancy test and a radiological assessment of the tumor. Tumor response is monitored with imaging at 4- to 8-week intervals. Hematological tests and serum chemistries are evaluated at 1- to 4-week intervals, and adverse events are collected continuously. Research blood tests are collected at the times of tumor evaluations. Dose adjustments are carried out as per the protocol. Patients who benefit from the study treatment will be treated with PTK787ZK222584 until treatment failure. 