A patient with acromegaly and hyperthyroidism due to a growth hormone-, thyrotrophin- and alpha-subunit-secreting pituitary adenoma is described. His decreased father had suffered from a pituitary tumour, and was likely to have had acromegaly as well. Plasma growth hormone and insulin-like growth factor I concentrations were elevated, with levels between 10 and 20 micrograms/l and 4.4 and 7.3 kU/l, respectively. In spite of hyperthyroidism (free thyroxine, 45 pmol/l; free triiodothyronine, 24 pmol/l), plasma thyrotrophin remained at 2.8 mU/l without any response to thyrotrophin-releasing hormone and could not be suppressed with exogenous administration of triiodothyronine. Plasma alpha-subunits were raised to 3.3-3.7 U/l (normal 0.4-1.1 U/l). Pathological examination of the surgically removed tumour showed a pituitary adenoma with the immunohistochemical presence of growth hormone, thyrotrophin, prolactin and alpha-subunit. This is the first report of a growth hormone-, thyrotrophin- and alpha-subunit-producing pituitary adenoma, which occurred in a familial setting.