Choroid plexus of rabbit and rat was incubated for 2-30 min at 37 degrees C under 95% O2-5% CO2 in Tyrode solution containing 10 mM glucose and 1 mM theophylline with these agents: epinephrine, norepinephrine, isoproterenol, dopamine, histamine, serotonin, arginine, and lysine vasopressins, oxytocin, angiotensin, adrenocorticotropin (ACTH), beta-melanocyte-stimulating hormone, and choroid plexus peptide IIF. After incubation, tissue and medium were analyzed for 3', 5' -cyclic adenosine monophosphate (cAMP) content. Each amine or peptide was tested initially at 1,000 microng/ml. Only ACTH and serotonin affected cAMP content of rabbit choroid plexus. At 1,000 microng/ml, these agents caused a 10 and 4 times (respectively) increase in cAMP content of tissue + medium at 2-10 min with decline in content at 10-30 min. More than 90% of the increment was located in tissue, less than 10% in medium. Minimal effective dose (MED) to cause a significant (P less than .05) accumulation of cAMP was 0.1 microng/ml (2.2 x 10(-8) M) for ACTH and 10 microng/ml (5.7 x10(-3) M) for serotonin. Only isoproterenol, epinephrine, and norepinephrine influenced cAMP content of rat choroid plexus. MED's for this effect by isoproterenol, epinephrine, and norepinephrine were .001, .01, and 10 microng/ml (4.7 x 10(-9), 5.5 x 10(-8), and 5.9 x 10(-5) M), respectively.