In order to assess the presence of morphologically recognizable colonic nonneoplastic mucosal alterations that may be associated with adenomatous transformation the authors undertook a retrospective analysis of 984 colonic polyps removed between 1979 and 1983. There were 708 adenomatous and 276 nonadenomatous polyps, all colonoscopically removed. In addition to adenomatous mucosa, three different mucosal patterns were recognized and labeled as transitional, eosinophilic, and, hyperplastic. Each polyp, but not the polyp's shoulder, was scored by two pathologists for the presence of these changes. Analysis of the data (Pearson's chi-square test) demonstrated a strong association between eosinophilic and transitional mucosa as well as between eosinophilic mucosa and adenomas. There was also a strong negative association between both eosinophilic and transitional mucosa and hyperplastic mucosa. On the basis of these data, it is postulated that transitional mucosa, representing a nonspecific reactive mucosal phenomenon, may precede eosinophilic mucosa, which subsequently may represent fertile soil for adenomatous transformation.