In order to study the hormonal characteristics of human prolactin-secreting pituitary adenomas, in vitro monolayer and suspension cultures from human pituitary glands were established. Optimal conditions for cultures included enzymatic dispersion into viable single-cell suspensions with the use of 1% collagenase in phosphate-buffered saline solution. After pelleting the dispersed cells by centrifugation (800 rpm for 10 minutes), they were cultured in RPMI medium that contained 20% fetal calf serum and then incubated at 37degrees C in 5% CO2. Cells were subcultured weekly at a ratio of one plate to two. In an attempt to establish whether bromocriptine has a direct inhibitory effect on pituitary secretion of prolactin (PRL), variable doses of bromocriptine were added to duplicate plates. The addition of bromocriptine to the culture medium induced suppression of PRL within 7 days. In conclusion, this study demonstrated that either monolayer of suspension cultures of human PRL secreting adenomas can be established, and that bromocriptine in doses of 1 ng/plate or more has a direct inhibitory effect on the secretion of PRL.