In this study both prostaglandin A1 (PGA1) and prostaglandin F2alpha (PGF2alpha) have been shown to be effective long-lasting stimulators of the cyclic AMP (cAMP) synthesis in the liver, intestinal mucosa and brain, whereas prostaglandin E1 (PGE1) was found to have a similar effect on the cerebral cAMP synthesis and a dissimilar effect (decrease) on the hepatic one. A lack of sensitivity of the intestinal mucosa cAMP to PGE1 was also observed.