A previous study reported the expression of functionally impaired thyroid hormone receptor (TR)beta1 mutants in almost all papillary thyroid carcinomas. To confirm this, we analyzed the sequence of the entire coding region of TRbeta1 cDNAs expressed in 16 papillary carcinomas. Among the 48 clones analyzed, we found no mutations with an amino acid substitution, which represents a clear discrepancy between our findings and those in the previous study. Our findings suggest that the expression of functionally impaired mutants in papillary carcinomas is rare, and they raise a question about the possible role of mutated TRbeta1 in the tumorigenesis of papillary carcinoma.