Basal and modulated secretion of PRL and GH by dispersed cell cultures of human somatotropic, lactotropic, and mixed somatotropic-lactotropic adenomas has been examined. Twenty-four-hour secretion of PRL by a normal pituitary, a lactotropic, and a mixed adenoma increased with time in culture. The secretion rate from a mixed adenoma had increased 18-fold by day 20 over that observed on day 1, 225 µg PRL being produced from 4 X 105 cells. PRL secretion was still elevated after 36 days of culture. GH secretion always decreased rapidly from day 1. Initial GH secretion in cultures of a somatotropic adenoma was 18-fold of that from the same number of normal pituitary cells. Theophylline (10-2 M) significantly stimulated GH secretion by somatotropic and mixed adenoma cells during a 4-h incubation after 4 and 28, but not 49, days in culture. PRL secretion was only stimulated at 28 days. TRH stimulated PRL and GH secretion from adenomas in a dose-dependent manner, with 10 ng/ml TRH being maximal. Somatostatin alon...