Our recent study of the gene expression profile in thyroid carcinoma showed an overexpression of osteonectin mRNA, an extracellular matrix protein, in an anaplastic carcinoma. To confirm this, we measured the expression levels of osteonectin mRNA in 84 thyroid normal and tumor tissues, including five anaplastic carcinomas by realtime quantitative reverse-transcription PCR. Increased expression of osteonectin mRNA was observed in anaplastic carcinoma tissue. However, in five anaplastic carcinoma cell lines, no increase was observed in the expression levels of osteonectin mRNA. These findings suggest the possibility that increased expression of osteonectin mRNA in anaplastic carcinoma tissue may be due to its overexpression in stromal cells, but not in anaplastic carcinoma cells.