Background and aim of the study : the diagnosis of malignancy in the upper GI tract may be difficult to determine at histological examination, especially if diffuse, infiltrative or submucosal lesions are sampled using a standard, 7-Fr, biopsy forceps. We report on the results obtained with a new, larger, biopsy forceps in patients with such lesions, of undefinite diagnosis at anatomopathological examination of biopsies obtained using a standard forceps. Patients and methods : between 11/97 and 10/99, 27 patients were assessed for this technique (13 men and 14 women ; mean age, 60 ± 14 years). All patients disclosed at upper GI endoscopy a lesion whose histological diagnosis remained indefinite after examination of standard biopsies (sampled using a 7-Fr forceps). Macrobiopsies were sampled using a 15.3-Fr forceps (FB-51K-1, Olympus, Hamburg, Germany) passed through the 6-mm working channel of a jumbo fiberoptic gastroscope (XT-30, Olympus). Diagnosis was confirmed by surgery or by adequate follow-up. Results : endoscopic examination disclosed mucosal ulcers or nodules in 15 patients, submucosal nodules or large polypoid lesions in 11 patients, as well as large ulcerated folds in the duodenum of 1 patient. No complication related to the sampling procedure was observed. Histological examination of macrobiopsies provided a definite diagnosis of malignancy in 14 patients (lymphoma, n=3 ; adenocarcinoma in Barrett's esophagus, n=3 ; squamous epithelioma, n=1; linitis gastrica, n=4 ; carcinosarcoma, n=1 ; melanoma, n=1 ; metastasis, n=1), a diagnosis of benign submucosal tumour in 1 patient, and confirmed the absence of tumour in 9 others (by evidencing normal mucosa and submucosa). In 4 patients, including 2 leiomyoma, macrobiopsies failed to reveal the diagnosis. Submucosa was evidenced in macrobiospies from 27/27 (100%) patients, compared to standard biopsies from 6/27 (22%) patients (<0.001). Conclusions : the use of a 15.3 Fr biopsy forceps significantly increases the yield of histological diagnosis for lesions located in the upper GI tract, especially if these are infiltrative or located in the submucosa.