Summary Serial thyroid functions studies were carried out in patients with melanoma and renal cell carcinoma treated with interleukin-2 (3 MU m-2 by continuous infusion days 1-4) and interferon a-2a (6 MU m-2 subcutaneously on days 1 and 4), both given on alternate weeks. The results on eight patients who completed at least three cycles of treatment are described. Four patients developed thyroid dysfunction with a hyperthyroid phase of 2 weeks followed by a hypothyroid phase ranging from 12 to 24 weeks. Two patients became clinically symptomatic and required treatment. Fine-needle aspirates of the thyroid were obtained in three patients with thyroid dysfunction. The considered to be 0-350 IE ml-' with 350-500 U ml-' borderline and > 500 IE ml-X elevated. Levels of anti-nuclear, anti-mitochondrial, anti-parietal and anti-islet cell antibodies were measured by indirect immunofluorescence (Kit from Zeus Scientifics Inc., Raritan, NJ, USA, and DMD AG, Schaffhausen, Switzerland).Cytological studies Fine-needle aspirations were done in three patients with thyroid dysfunction using a 25-gauge needle and a 20 ml disposable syringe in a Cameco-holder. The