Different juvenile hormone mimics were compared regarding their efficacy against larval and pupal stages of the diptera Aedes aegypti, Musca domestica, and Lucilia cuprina as well as the cat flea Ctenocephalides felis. Structure-activity relationship of a series of new diphenylethers was analyzed and compared to juvenoids like methoprene, hydroprene, and fenoxycarb. Selected compounds were taken for a competition binding assay and their effect on JH-degradation by esterases was examined. The results indicate that neither high affinity to JH-binding proteins nor interference with JH breakdown are responsible for the extraordinary efficacy of the diphenylethers investigated. Two superior diphenylethers, however, proved to be more resistant to UV-radiation than methoprene.