The past few years have seen an increasingly tight link between grid computing and Web services, with the latest standards defining a grid computing architecture as a set of services built using Web services standards and protocols. However, the reputation of these technologies (SOAP, XML, WSDL, HTTP) is that they are heavyweight and slow, something that is potentially a concern given the current and anticipated application mix for high performance grid architectures. This paper reports the results of a performance evaluation carried out on Globus 3.9.4, a reference implementation of the new GGF standards that are built on the Web services resource framework (WSRF). The evaluation approach combines low interference measurement (black box) techniques with more sophisticated sampling-based profiling (gray box) techniques. The results indicate possible opportunities for optimization, as well as provide useful input for the designers of grid services.