Sensitivity of Vibrio species especially ofVibrio parahaemolyticusagainst various pteridine derivatives were examined. 2: 4 diamino 6: 7 di-n-propyl pteridine (O/69) has the vibriostatic activity as well as 2: 4 diamino 6: 7 di-iso-propyl pteridine (O/129), which is recognised as vibriostatic agent.2: 4 diamino 6: 7 di-iso-propyl pteridine synthesized by Dr. Saikachi was equally active as vibriostatic agent (O/129) and the possibility of itssynthesis in our country was discussed