Thyroid function was studied in 27 subjects who underwent bronchography with propyliodone (18-70 ml, containing 30% of organic iodine). Sustained elevations of serum non-hormonal iodine were observed, indicating that significant amounts of propyliodone were absorbed from the bronchial tree and also that elimination may take several weeks. During the period of anaesthesia, there was an increase in thyroxine-binding globulin and all thyroid hormones which was transient and probably reflected vascular response to the anaesthetic. T4-T3 conversion was inhibited with a nadir of T3 and a peak of rT3 occurring on the 2nd day after propyliodone exposure. FT4 increased gradually during the 2 weeks after bronchography, but remained within the normal range. 6 out of the 27 patients developed pathologic T4 levels, 3 elevated T3 levels, and 2 an abnormal response to thyrotropin-releasing hormone; these changes might have been confused with hyperthyroidism. None of the patients developed clinical thyrotoxicosis; however, in patients with autonomous thyroid tissue, the same precautions should be taken with propyliodone as with other iodine-containing agents which are known to induce hyperthyroidism in this situation.