The presumptive diagnosis of gastric submucosal tumors can be made by endoscopic ultrasonography (EUS) but histological confirmation is still required. A special guillotine biopsy device (Flexi-Temno) which enables collection of adequate submucosal samples by the endoscopic approach was therefore evaluated. After visualization by EUS the guillotine needle biopsy was performed in 21 patients with submucosal tumors of the stomach. There were 2 failures in 2 patients with leiomyomas. The diagnosis suggested by EUS was confirmed by guillotine biopsy in 17 cases. Guillotine biopsy detected 2 cases of unsuspected leiomyosarcoma which were confirmed surgically. In cases of solid submucosal tumors confirmed on EUS, the guillotine needle biopsy enables a definitive histologic diagnosis. Thus malignancies can be detected when EUS findings are not significant.