A primary benefit of Web Services is that they provide a uniform implementation-independent mechanism for accessing distributed services. Building and deploying such services do not benefit from the same advantages, however. Different Web Services containers are implemented in different programming languages, with different constraints and requirements placed on the programmer. Moreover, client side programmers must use the Web Service interface specified by the service developer. Therefore, the kinds of applications and uses for a Web Service are unnecessarily restrictive, constrained by the granularity of access defined by the interface and by the characteristics of the service functions. This paper describes an approach that addresses both of these drawbacks by enabling Web Service containers with the ability to accept new mobile code on the fly, and to run it within the containers, providing direct local access to the containers' other services. The code can be specified in a small simple language (a subset of C), and translated and passed to the container in a common XML-based intermediate language called X#. This approach effectively removes the dependence on any single implementation environment. Our prototype implementation for two different containers demonstrates the feasibility of the approach, which represents a first step toward write-once deployanywhere Web Services.