Human functioning pituitary adenomas (3 acromegalies, 3 prolactinomas) obtained at transsphenoidal hypophysectomy were dispersively embedded inside collagen gels and subjected to the conventional monolayer culture in Eagle's MEM medium containing fetal bovine serum. Basal secretion of growth hormone (GH) and prolactin (PRL) in the media of monolayer and collagen gel cultures were measured by radioimmunoassay (RIA) for 5 weeks. GH secretion in the culture media was initially high in all cases with acromegaly in both monolayer and collagen gel cultures. GH secretion in monolayer culture declined rapidly almost as a straight line on a semilogarithmic scale until 5 weeks, when GH level decreased around 10 ng/ml. GH secretion in collagen gel culture was preserved more than in monolayer culture, but declined slowly up to about 500 ng/ml within 5 weeks. PRL secretion in monolayer culture initially declined rapidly until 1 week, but after then remained constant or decreased slowly. In the other hand, PRL secretion in collagen gel culture remained almost constant for up to 5 weeks. It is concluded that this new culture method may provide suitable conditions for maintenance of the adenomas cells in vitro.