Product systems are the classifying structures for 
semigroups of endomorphisms of B(H), in that two 
E_0-semigroups are cocycle conjugate iff their 
product systems are isomorphic.  Thus it is important 
to know that every abstract product system is associated 
with an E_0-semigroup.  This was first proved more than 
fifteen years ago  by rather indirect methods.  
Recently, Michael Skeide has given a more direct proof.  
In this note we give yet another proof by an elementary 
construction.