A total of 117 colorectal tissue specimens were examined immunohisto-chemically for the production of immunoreactive (IR-) transforming growth factor (TGF)-a and IR-epidermal growth factor (EGF). IR-TGF-a was detected in 26/32 (81.3%) invasive cancers, 14/27 (51.9%) carcinomas in situ, and 14/58 (24.1 %) adenomas. IR-EGF was detected in 14/32 (43.8%) invasive cancers, 12/27 (44.4%) carcinomas in situ, and 12/58 (20.7%) adenomas. The staining intensity of IR-TGF-α was related to the histologic grade of malignancy, but that of IR-EGF was not. These suggest that IR-TGF-α plays a more important role than IR-EGF in the growth of colorectal neoplasms, and that further study of these growth factors would be helpful in understanding the biology of colorectal carcinoma.