The effects of biogenic amines on the formation of adenosine-3′,5′monophosphate (cAMP) in the anterior pituitary of rats were investigated. Pituitary halves were pre-incubated in a Krebs-Ringer bicarbonate buffer (pH 7.4) containing theophylline (10^-2M) at 37°C for 30 minutes and incubated in a fresh buffer for 15 minutes after the addition of test substances. Noradrenaline at 4×10^-4M and serotonin at 3.3×10^-4M were effective in elevating cAMP, but dopamine at 2×10^-4M was ineffective. The β adrenergic blocking agent, propranolol, effectively antagonized the cAMP response to noradrenaline, but the α adrenergic blocking agent, phentolamine, did not. The serotonin antagonist, methysergide, remarkably antagonized the cAMP response to serotonin, but the α and β adrenergic agents did not.