This paper presents a novel approach to the problem of finding all subgraph isomorphisms of a (pattern) graph into another (target) graph. A relational formulation of the problem, combined with a representation of relations and graphs by Boolean functions, allows to handle the combinatorial explosion in the case of small pattern graphs and large target graphs by using Binary Decision Diagrams (BDDs), which ar= e capable to represent large relations and graphs in small data structures. Examples are presented that show how all subgraph isomorphisms (120303) of = a small graph into a large graph can be efficiently computed and represented with a small BDD (57980 nodes).