Antagonistic peptides of GnRH having improved water solubility are disclosed. These peptides are capable of suppressing serum testosterone levels in vivo to chemical castration levels of ≦0.5 ng/ml. Stable, filter sterilizable, non-gelling solutions containing the GnRH antagonists at least at levels typically used in sustained release formulations also are disclosed, as is a method of increasing the solubility of GnRH antagonist in a polymer containing dispersed phase, which method comprises addition of an acid to the dispersed phase.
