The effects of handling, ether vapor anesthesia and blood sampling on serum LH and prolactin were determined in intact, castrate and dexamethasone-treated male rats. Cage removal and transport to an adjacent room increased LH and prolactin levels by 10 and 15 min after the initial animal disturbance. Intact male rats subjected to repeated ether anesthesia and blood sampling showed a more rapid increase in serum LH and prolactin than the preceding rats, since serum LH and prolactin was increased by 4, 8 and 15 min after initial cage disturbance. In a group of rats subjected to serial blood sampling over a longer time interval, both prolactin and LH levels remained higher than 90 min after initial animal handling. At 90 minutes after a single blood sampling, blood prolactin concentration remained higher than in controls. Serum LH levels returned to control levels 90 min after the stress of a single blood sampling. Although serum prolactin was increased in the castrate group subjected to serial anesthesia and blood sampling, LH concentrations were reduced under the same conditions. Injection of 5 and 50 mug of dexamethasone/100 g body wt for 8 days markedly reduced adrenocortical responsiveness to the stress of serial anesthesia and blood sampling at 1, 4, 8 and 15 min after initial rat disturbance. The 50 mug dexamethasone treatment reduced the stress-stimulated increase in serum prolactin at all blood sampling intervals. The dexamethasone-treated groups also showed smaller increases in serum LH at 8 and 15 min after first animal handling than the control rats. These results indicate that serum LH and prolactin concentrations are consistently increased by acute stress in intact male rats, the duration of the stress stimulation of LH and prolactin is at least 90 min under the conditions of this study, serum LH levels of castrate male rats are decreased by acute stress and dexamethasone administration lowers stress stimulation of LH and prolactin release.