To demonstrate whether or not fine needle aspiration biopsy caused release of thyroglobulin into the circulation and if there was a correlation between histological diagnosis and thyroglobulin release from thyroid during aspiration, serum thyroglobulin concentrations were determined in 12 patients with solitary cold nodule or multinodular goitre. Of the 12 patients studied, seven had significant (P less than 0.05) elevations of serum thyroglobulin after aspiration. It is suggested that circulating thyroglobulin may increase after minor trauma to thyroid tissue such as following fine needle aspiration.