Thyroid papillary carcinomas are well-differentiated cancers, but frequently invade surrounding tissue and metastasize to the regional lymph nodes However, biological studies of thyroid papillary carcinoma have been infrequently done because of their good prognosis. For the purpose of understanding the biologic behavior of thyroid papillary carcinoma, the authors performed the immunhistochemical staining for epidermal growth factor receptors and neu, pan-ras oncoproteins in 35 cases of thyroid papillary carcinoma. The results were as follows : 1) Overall positive expression rate for epidermal growth factor receptors and neu, pan-ras oncoproteins were 62.9%, 97.1% and 31.4%, respectively. 2) The larger the size of primary tumor, the higher the positie expression rate for pan-ras oncoprotein. 3) There was no relationship between patient's age, thyroid capsular involvement, lymph node metastasis and positive expression rate for epidermal growth factor receptor and neu, pan-ras oncoproteins.