To demonstrate the correlation between the nanostructure formation and the long duration of action in vivo of peptides,the morphology of nanostructures of LXT-101,a novel synthetic amphiphilic peptide of gonadotropin-releasing hormone antagonist were observed by transmission electron microscopy when dissolved in different solvents.The plasma concentrations of LXT-101 [1] and testosterone levels [2] were also assayed for different solutions after intramuscular injection administration in beagle dogs to investigate the long-acting properties in vivo.TEM data suggest that LXT-101 in pure water can form fibres,while in mannitol,dextrose or sodium chloride solution,they tend to form vesicles.