Two female patients aged 46 years and 30 years presented with acromegaly. Chest radiographs revealed abnormalities which proved to be carcinoid tumours. Following surgical removal of these tumours immunoreactive human growth hormone (I.R.H.G.H.) in the serum suppressed normally with oral2 glucose. One of the tumours contained 225,000 μU/g wet weight of I.R.H.G.H. Both patients have shown clinical improvement. The implications are discussed.