Fourteen cases of intestinal-type adenocarcinomas (IADC) of the nasal cavity and paranasal sinuses were studied at the Regional Hospital of Varese during the period from 1973 to 1988. They were 13 males and 1 female, mean age 57.5 years; the five year survival was 25% and tumors were preferentially located in the ethmoidal sinus. Morphological study and the use of monoclonal and polyclonal antibodies made it possible to define the structural features of IADC and to detect specific antigenic markers such as CAR-5 (a glycoprotein contained within intestinal goblet-cells) and M1 (a glycoprotein contained within gastric foveolar cells). For comparison 10 cases of colonic adenocarcinomas and 14 cases of non-AIDC carcinomas of the nose and paranasal sinuses were also examined. The parallel morphological and immuno-histochemical investigations based on specific markers demonstrated that it was impossible to differentiate IADC from large bowel adenocarcinoma for both the structural pattern and antigenic expression. Moreover, AIDC also showed a CAR-5 and M1 immunoreactivity (IR) different from that displayed by the nasal carcinomas of different histotypes. From a histopathological standpoint IADC appears to be a distinctive entity even when compared to salivary gland tumors. In addition, the present immunohistochemical investigation demonstrates that gastric and intestinal glycoproteic antigens (M1 and CAR-5 respectively) occur in the normal nasosinusal mucosa. Both CAR-5 and M1 were observed in the mucous produced by nasal goblet cells with a distribution pattern resembling that of colonic goblet cells. Therefore, the present data confirm the similarity between nasal and colonic goblet cells which has already been pinpointed in previous morphological and ultrastructural studies. The common antigenic expression shared by the naso-sinusal and colonic mucosa might suggest a histogenetic hypothesis alternative to those of the malformative or metaplastic origin of naso-sinusal IADC.