Fourteen 4,4'-m-phenylene- and two 4,4'-p-phenylene-bis-sydnone imine hydrochlorides have been synthesized. All compounds exhibited good solubility in water. In the m-series the 3-(3-phenylpropyl)-derivative 5c and the 3-hexyl compound 5l showed antiplatelet activities at or below 10 mumol/L (IC50, Born-test with collagen). The corresponding p-compounds had the same (6l) or slightly lower (6c) activity. No effect on the fibrin formation (Quick-test) could be observed.