Chromogranin-A-positive pituitary adenomas include glycoprotein hormone-producing adenomas, null cell adenomas, and a few other pituitary adenomas. We studied the effects of GnRH, CRF, dexamethasone, and phorbol 12-myristate 13-acetate on FSH and LH secretion and on FSH beta and chromogranin-A and -B mRNA expression in 10 chromogranin-A-positive adenomas in vitro to analyze the regulation of FSH and chromogranin-A and -B expression in these neoplasms. Most adenomas responded to GnRH stimulation during 7 days in culture with a 2- to 10-fold increase in FSH and LH secretion and a 2- to 7-fold increase in FSH beta mRNA compared to control values. CRF and phorbol 12-myristate 13-acetate also stimulated FSH and LH secretion 2- to 5-fold in five of seven and three of three cases, respectively, during 7 days in culture. Dexamethasone stimulated both FSH and LH secretion in two of three cases as well as FSH beta mRNA in vitro in the one case examined. GnRH treatment consistently produced a 2-fold increase in chromogranin-B mRNA, but not in chromogranin-A mRNA, after 7 days of culture. These results indicate that many chromogranin-A-positive adenomas respond to GnRH and CRF in vitro by increased hormone secretion and that GnRH stimulation leads to increased amounts of FSH beta and chromogranin-B mRNAs. The differential response of chromogranin-A and -B mRNAs after GnRH stimulation indicates that the chromogranin genes are highly regulated in these tumors.