1. Isolated salivary glands of Calliphora have been used as a system on which to study the mode of action of a hormone.

2. Cyclic AMP, which is thought to mediate the action of many different hormones, can stimulate fluid secretion equally as well as 5-HT.

3. Methyl xanthines, which inhibit the hydrolysis of intracellular cyclic AMP by phosphodiesterase, can stimulate secretion and prolong recovery time after removal of 5-HT.

4. Methyl xanthines can sensitize salivary glands to both 5-HT and cyclic AMP.

5. Butyryl derivatives of cyclic AMP can stimulate secretion, but their effect is slower and lasts longer.

6. Certain amino acids and malate support fluid secretion more effectively than trehalose or glucose.

7. It is concluded that cyclic AMP plays an important role in the ability of 5-HT to control fluid secretion by salivary glands.

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