Piperazine derivatives have been identified as new antidiabetic compounds. Structure-activity relationship studies in a series of 1-benzyl-4-alkyl-2-(4′,5′-dihydro-1′H-imidazol-2′-yl)piperazines resulted in the identification of 1-methyl-4-(2′,4′-dichlorobenzyl)-2-(4′,5′-dihydro-1′H-imidazol-2′-yl)piperazine, PMS 812 (S-21663), as a highly potent antidiabetic agent on a rat model of diabetes, mediated by an important increase of insulin secretion independently of R 2 adrenoceptor blockage. These studies were extended to find additional compounds in these series with improved properties. In such a way, substitution of both piperazine N atoms was first optimized by using various alkyl, branched or not, and benzyl groups. Second, some modifications of the imidazoline ring and its replacement by isosteric heterocycles were carried out, proceeding from PMS 812, to evaluate their influence on the antidiabetic activity. The importance of the distance between the imidazoline ring and the piperazine skeleton was studied third. Finally, the influence of the N-benzyl moiety was also analyzed compared to a direct N-phenyl substitution. The pharmacological evaluation was performed in vivo using glucose tolerance tests on a rat model of type II diabetes. The most active compounds were 1,4-diisopropyl-2-(4′,5′-dihydro-1′H-imidazol-2′-yl)piperazine (41a), PMS 847 (S-22068), and 1,4-diisobutyl-2-(4′,5′-dihydro-1′H-imidazol-2′-yl)piperazine (41b), PMS 889 (S-22575), which strongly improved glucose tolerance without any side event or hypoglycemic effect. More particularly, PMS 847 proved to be as potent after po (100 µmol/kg) as after ip administration and appears as a good candidate for clinical investigations.