Summary: A case of acromegaly complicated by pituitary apoplexy is described. The pituitary apoplexy occurred while the patient was under investigation in a metabolic ward permitting full assessment of pituitary function both before and immediately after the event. This demonstrated a remarkably selective reduction in the plasma growth hormone concentration with preservation of other pituitary function excluding mild diabetes insipidus. The plasma growth hormone fell from values greater than 120 ng/ml to less than 4 ng/ml. The brisk inappropriate release of growth hormone observed on stimulation with thyrotrophic hormone releasing hormone, associated with a severe headache and the onset of pituitary apoplexy two days later raised the possibility of provocative tests of pituitary function precipitating pituitary apoplexy.