Let G be a (p,q) graph. An injective map ƒ: V (G) →{±1, ±2,...,±p} is called a pair sum labeling if the induced edge function, ƒ e : E(G)→Z -{0} defined by ƒ e (uv)=ƒ(u)+ƒ(v) is oneone and ƒ e (E(G)) is either of the form {±k 1 , ±k 2 ,…, ±k q/2 } or {±k 1 , ±k 2 ,…, ±k (q-1)/2 } {k (q+1)/2 } according as q is even or odd. Here we prove that every graph is a subgraph of a connected pair sum graph. Also we investigate the pair sum labeling of some graphs which are obtained from cycles. Finally we enumerate all pair sum graphs of order ≤ 5.