It is not clear whether the pre-operative treatment of GH-secreting pituitary adenomas with Octreotide improves the surgical remission rates of acromegaly. In a prospective controlled study the results off transsphenoidal surgery in newly diagnosed OH-secreting macroadenomas were compared in patients with (n = 11, group A) and without (n = 13, group B) preoperative Octreotide treatment. During the treatment with a daily dosage of 470 +/- 160 mu g Octreotide for 16,5 +/- 10 weeks, the GH- and IGF-1-values of group A dropped significantly from 38,9 +/- 34,1 to 6,8 +/- 4,9 mu g/l and from 2,7 +/- 1 to 1,7 +/- 0,7 arbitrary units respectively. The adenoma-shrinkage from 5,9 +/- 5,8 to 4,7 +/- 4,9 cm(3) missed statistical significance by little. There was no statistically significant difference between the postoperative acromegaly remission rates of 55% in group A and 69% in group B. Of the adenomas that postoperatively were not in remission, 80% in group A and 75% in group B disclosed an infiltrative growth pattern not influenced by the Octreotide pretreatment. All other patients not cured presented with initial GH-values of > 50 mu g/l. There was no statistically significant difference between the postoperative anterior pituitary function in the two patient groups. In this study Octreotide was not beneficial in improving the results of GH-secreting pituitary macro-adenoma surgery. However, larger prospective controlled studies are needed to address this issue.