Hyperplastic polyps are considered to be benign colonic lesions with almost no potential for malignant transformation. Recent reports have shown an increased association of hyperplastic polyps with adenomatous polyps and have advocated a full colonoscopy in patients who harbor hyperplastic polyps. Hyperproliferative mucosa is known to be associated with adenomatous polyps, but its relationship to hyperplastic polyps is unknown. In the present pilot study, it is determined whether a change in mucosal proliferative patterns is observed in patients who harbor only hyperplastic polyps or a history of hyperplastic polyps relative to those who harbor both hyperplastic polyps and adenomatous polyps by measuring ornithine decarboxylase and tyrosine kinase activity in macroscopically normal rectal mucosa. Fifteen patients had either adenomatous polyps proximally or harbored adenomatous polyps and hyperplastic polyps. Seven patients had hyperplastic polyps and 15 patients had a prior history of hyperplastic polyps with no polyps found during the current examination. The ornithine decarboxylase activity of the rectal mucosa with proximal adenomatous polyps or both polyp types was significantly higher than that of hyperplastic polyps, the history of hyperplastic polyps, or controls, and values for hyperplastic polyps and the history of hyperplastic polyps were similar to controls. On the other hand, tyrosine kinase activity in the rectal mucosa of patients with both or either polyp type was elevated without any significant difference between hyperplastic and adenomatous polyps. Thus, it is concluded that although increased ornithine decarboxylase activity in rectal mucosa suggests the presence of adenomatous polyps or a combination of adenomatous with hyperplastic polyps, increased tyrosine kinase activity suggests the presence of any type of polyp.