Oral administration of 1.0 or 2.5 mg bromocriptine (CB 154: 2-brom-alpha-ergocryptine) in nine of twelve patients with active acromegaly resulted in a reduction of growth hormone level by 80-90% over 8-10 hours. During treatment for 2-9 months with daily doses of 4.0 to 10.0 mg bromocriptine, there was a sustained reduction of growth hormone levels in these patients. At the same time soft-tissue swellings and tendency towards sweating decreased. In two patients with diabetes mellitus the blood sugar profile improved and in one of them the insulin dose could be markedly reduced. The rise in growth hormone levels after TRH administration also occurred during bromocriptine treatment. In those patients in whom growth hormone levels failed to react to either acute or chronic administration of bromocriptine no rise followed TRH administration. It is possible that in these patients there is a hypophyseal adenoma without hypothalamic control. On gradually increasing dosage bromocriptine was tolerated without side effects.