JBossWS may perform differently during the first method invocation of each service and the following ones when huge wsdl contracts (with hundreds of imported xml schemas) are referenced. This is due to a bunch of operations performed internally during the first invocation whose resulting data is then cached and reused during the following ones. While this is usually not a problem, you might be interested in having almost the same performance on each invocation. This can be achieved setting the org.jboss.ws.eagerInitializeJAXBContextCache system property to true, both on server side (in the JBoss start script) and on client side (a convenient constant is available in org.jboss.ws.Constants). The JAXBContext creation is usually responsible for most of the time required by the stack during the first invocation; this feature makes JBossWS try to eagerly create and cache the JAXB contexts before the first invocation is handled.