We studied immunohistochemical reactions to vimentin, desmin and protein S-100 in 43 cases of stromal tumors of the gastrointestinal tract. The material studied included: 1 esophageal tumor, 18 gastric tumors, 19 small intestinal tumors and 5 colonic tumors, classified in 13 cases as benign and in 30 cases as malignant neoplasms of various degree of malignancy. Mean age of the patients was 58.9 years. A positive reaction to vimentin was found in 37 cases, a negative reaction concerned an esophageal tumor, two benign tumors (gastric and small intestinal) and three malignant tumors (gastric and two small intestinal). A positive reaction to desmin was detected in an esophageal tumor and in nine gastric tumors. Only one benign small intestinal tumor and three benign colonic tumors showed a positive reaction to desmin. Protein S-100 was found in an esophageal tumor and in 7 out of 18 gastric tumors and in 12 out of 24 intestinal tumors. Coexpression of vimentin and desmin was found in 8 gastric tumors, only in one small intestinal tumor and in three colonic tumors. Three gastric tumors showing both these reactions were all benign. Coexpression of desmin and protein S-100 was found in 7 out of 43 tumors of the alimentary tract. In six cases these tumors were benign. Basing on the results we may say that the presence of these antigens reflects the degree of differentiation of gastrointestinal stromal tumors of the gastrointestinal tract, though it does not allow to choose unequivocally conclusions as to their histogenesis.