Aggregative amoebae of Dictyostelium discoideum, D. mucoroides, D. purpureum, and D. rosarium react chemotactically to cyclic AMP (cAMP). We measured the chemotactic activity of 14 cAMP analogs and found that these four species have a similar sensitivity to chemical modifications of cAMP; this suggests that the cAMP receptor is identical in all of these species. Besides the induction of a chemotactic response, cAMP analogs also may delay or prevent cell aggregation. cAMP analogs like N1-O-cAMP, 2'-H-cAMP, and 5'NH-cAMP are chemotactically nearly as active as cAMP and induced no, or only a short, delay of cell aggregation. Other cAMP derivatives, such as 6-Cl-cPMP and 8-Br-cAMP, are chemotactically active only at high concentrations and delayed cell aggregation for several hours. Still other cAMP analogs, which do not induce a chemotactic reaction in D. mucoroides, D. purpureum, and D. rosarium, either prevented cell aggregation [cAMPS(S), cAMPS(R), and 3'-NH-cAMP[ or had no effect on cell aggregation [cAMPN(CH3)2(S) and cAMPN(CH3)2(R)]. cAMP analog 3'-NH-cAMP prevented cell aggregation by the inhibition of chemotaxis, whereas cell locomotion was not affected. Although we cannot provide a satisfactory explantation for these observations, our data suggest that occupation and activation of the cAMP receptors do not always induced a chemotactic response.