With immunofluorescent techniques it has been possible to show that bound cyclic AMP is uniformly distributed in the nucleus and cytoplasm of a number of species of cellular slime molds. One species (which does not respond to cyclic AMP as an acrasin) is an exception and has its cyclic AMP concentrated in the nucleus during the feeding and aggregation stage. In cell masses of Dictyostelium discoideum that show early signs of differentiation the anterior, prestalk cells contain more cyclic AMP than the posterior, prespore cells.