A system and method for caching type information for parts (e.g., parameters) of an operation passed in a web service request. When an untyped request (i.e., a request in which the data types of operation parts are omitted) is received at a web service server from a client, a cache is examined to determine if type information for the requested operation's parts exists. If not, a cache entry specific to that operation is created and populate with the necessary type information (e.g., from a WSDL document corresponding to the web service). The type information for the operation, and any global type information (i.e., for data types global to the web service), is merged for use in unmarshalling the untyped request. The operation is invoked, and any results are returned to the client.