The Ag-NOR technique has been applied to many tissues in order to evaluate proliferative lesions. In colorectal mucosa dots counting is not reliable, but the analysis of their shape can be very useful for diagnosis. We applied the Ag-NOR technique to 71 smears of colorectal mucosa, classified in three groups according to the histopathologic diagnosis of the corresponding biopsies: normal/reactive (20 cases), low grade dysplastic mucosa/adenoma (six cases), adenocarcinoma (45 cases). In normal/reactive mucosa and in low grade dysplastic mucosa NORs were small dots, sometimes clustered or interlinked but with a homogeneous pattern. In the group of adenocarcinoma there was great variation in size and shape of NORs, bizarre forms, angulations, giving a heterogeneous pattern to the smear. Due to the large and characteristic variation in NORs of carcinomatous cells, they can be recognized as "malignancy markers", giving a good help for the diagnosis of some difficult cases in the daily practice.