Twenty-one patients with various types of pituitary macroadenomas underwent hypophysectomy at the Chaim Sheba Medical Centre between 1985 to 1987. Intraoperative fine needle aspiration of the tumoural content was attempted prior to tumour excision. Although none of the patients had a history compatible with pituitary apoplexy, intratumoural fluid suggestive of a cyst within the tumour was found in 57% of the patients. Analysis of the hormones in the aspirated fluid revealed variable elevations in hormone levels, some reaching 3,000 times the equivalent plasma levels. Concomitant elevated levels of other pituitary hormones found in the cyst fluid support the concept of mixed secretory potential of pituitary adenomas, including the apparently non-functioning tumours. Six out of seven patients (86%) who received preoperative treatment with bromocriptine had an intratumoural cyst while only seven out of fourteen patients (50%) who were not treated with this drug prior to surgery had a cyst within the tumour. The implications of these observations on current theories concerning the pathophysiology of pituitary adenomas are discussed.