Sixty patients with clinically and biochemically active acromegaly were treated by transsphenoidal surgery. All patients underwent a full assessment of pituitary function both preoperatively and postoperatively; these studies were repeated 6 months after surgery and every year, when possible. The mean follow-up period was 3.3 years (range 0.5-7 years). The GH level normalized in 62% of patients after surgery. A paradoxical reaction of GH to TRH was present in 35 patients before surgery and had normalized in 17 after surgery. Large tumours were associated with higher GH levels than smaller tumours. A prognostic factor in terms of normalization of both the GH level and an eventual paradoxical reaction to TRH or a glucose challenge was a low preoperative GH level. Three out of seven patients with either a positive postoperative TRH test but a normal GH level, or a slightly elevated GH level suffered a biochemical and clinical recurrence and two of them underwent reoperation. In contrast, when the TRH test had normalized (always in association with normal GH levels) no recurrence was found. The impact of surgery on the other pituitary functions was generally slight and the numbers of patients with preoperative and postoperative impairment were about equal. Postsurgical radiation therapy was administered to patients with an elevated GH level, a non-normalized TRH test irrespective of whether the GH level had normalized, or local invasion of the tumour. In 11 out of 17 patients with elevated GH levels after surgery, normalization was achieved by radiation therapy after a mean period of 2.7 years. The incidence of pituitary failure after irradiation appeared to be high; gonadal function in men and the GH reserve function were especially vulnerable. From this study we conclude that in many cases the adenoma can be removed effectively, without compromising the other pituitary functions. However, a substantial number of the patients require additional radiation therapy, leading to an inevitable loss of other pituitary functions.