The histological distribution of receptors for R. communis Fraction 1 (RCA1) in oral carcinomas and in oral epithelial cells during wound healing was studied by use of fluorescein-tagged RCA1. Biopsies from 15 human oral carcinomas and adjacent normal mucosa showed RCA1 receptors at the cell membranes in the basal and spinous layer of the normal epithelium, whereas receptors could not be demonstrated in invading islands of the tumors. In healing oral wounds from 8 humans and 3 rhesus monkeys, RCA1 receptors were demonstrated both in normal epithelium adjacent to the wounds and in the epithelial outgrowth from the wound margin. Titrations showed that the epithelial outgrowth reacted more weakly than did the normal adjacent epithelium. Previous in vitro studies show changes in carbohydrate composition of moving normal cells and of malignant cells. This may be of interest in relation to formation of metastases.