The precursors for colorectal cancer include polypoid (conventional), flat and serrated adenomas. Polypoid growth in polypoid adenomas and serrated adenomas is associated with K-ras mutations. The regulation of polypoid or nonpolypoid growth is not well known, but could be related to trophic stimuli, such as thyroid hormones. Hence, we investigated the expression pattern of thyroid hormone receptor TRbeta1 in colorectal mucosa and in colorectal tumours and its relationship to tumour growth type. One hundred fourteen colorectal carcinoma specimens were evaluated for TRbeta1. Normal mucosa, adjacent adenomatous component (N = 46) and lymph node metastases (N = 28) were analysed when present, and the results were confirmed by Western blot analysis in selected cases. Nuclear TRbeta1 was almost always present in normal epithelium (96%), but less frequent in adenomas (83%) and in cancer (68%; p