Control dependence information is useful for a wide range of software maintenance and testing tasks. For example, program slicers use it to determine statements and predicates that might affect the value of a particular variable at a particular program location. In the intraprocedural context an optimal algorithm is known for computing control dependence which unfortunately relies critically on the underlying intraprocedural postdominance relation being tree-structured. Hence, this algorithm is not directly applicable to the interprocedural case where the transitive reduction of the postdominance relation can be a directed acyclic graph (DAG), with nodes having multiple immediate dominators. In this paper we present two efficient, conceptually simple algorithms for computing the interprocedural postdominance relation that can be used to compute interprocedural control dependence. For an interprocedural control flow graph $G=(V,E)$, our reachability based algorithm takes time and space $O(|V|^2 + |V||E|)$. Unlike other algorithms, it does not perform confluence operations on whole bit-vectors and can be tuned to concentrate on the interprocedural rather than intraprocedural relations in a program thus allowing it to scale better to larger programs.