Plasma growth hormone (GH) concentrations were measured over 24 h in seven acromegalic patients before and during treatment with 2-bromo-alpha-ergocriptine (CB-154). Before treatment basal plasma GH levels were consistently elevated but no significant change was observed between the mean plasma GH levels during sleep and during waking in five of the seven patients examined. The daily administration of CB-154 (5 to 10 mg, orally) for 14 days resulted in a significant fall in the 24 h mean plasma GH levels in six of the seven patients. In all of the six patients who responded to CB-154 treatment, the mean plasma GH concentrations during sleep were significantly greater than during waking. Daytime sleep was associated with a significant rise in plasma GH in both of the two patients examined. It is concluded that CB-154 treatment resulted in a significant decrease in plasma GH levels with sleep-related increase in some acromegalics although the mechanism responsible for this sleep-related GH rise remains to be further investigated.