Abstract Phosducin (Phd), a cytosolic protein, has been proposed to compete with certain receptor kinases for Gβγ of heterotrimeric G proteins, and may inhibit GTPase activity of Gαs. These suggestions together with the enhancing effect of Phd on odorant-induced cAMP accumulation let us assume a stimulatory action of the protein on intracellular signaling. Therefore, this investigation was designed to examine the excitatory effect of PGE 1 on signal transmission in neuroblastoma x glioma hybrid cells (NG 108-15) overexpressing Phd. The neuronal cells stably expressing Phd were found to display a 3 to 4-fold increased sensitivity to PGE 1 as compared to wild type cells, using cAMP accumulation as measure. Examination of membranes prepared from Phd-overexpressing cells revealed an elevated GTPase activity as indicated by the formation of 32P i upon PGE 1 challenge. This activity was inhibited by exogenous Phd. In addition, receptor independent stimulation of adenylate cyclase by forskolin reveals an increased formation of cAMP in Phd expressing cells, which is accompanied by an increased binding of [ 3H]forskolin. The findings let us propose that Phd elevates intracellular levels of functional Gαs which accounts for the increased response to PGE 1.