A note on the complexity of finding regular subgraphs

Given a graph G and an integer r, does there exist a regular subgraph of G with degree r? In this note we establish NP-completeness for the r-regular subgraph problem for each r >= 3 and certain restrictions on G. In particular, the cubic subgraph problem is NP-complete even for the simple case where G is a bipartite planar graph with maximum degree 4.