Perin B3 is a quest item in S.T.A.L.K.E.R.: Call of Pripyat.
Perin B3 is a nerve gas that was supposed to be tested in the Zone. It is found in in Zaton, on the Preobrazhensky Bridge in a locked container. Two keys are required to unlock the container, both of which are nearby. This item is part of the Bloodsucker Lair purging quest.