Web applications and Web services have to undergo rapid modifications, and these modifications must be supported by rapid verification. While regression testing (RT) is a major component of most major testing systems, the related techniques have only just begun to be applied to Web services. One of the more important techniques, Regression test selection (RTS) aims to reduce the cost of performing RT. This paper reports a control flow graph-based approach that makes it possible to apply a safe RTS technique to Web services in an end-to-end manner. Safe RTS techniques ensure that no modification revealing tests will be left unselected. A simplified purchase order system that involves in three Web services is used to illustrate the use of our approach.