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We describe the design, implementation and experimental evaluation of a software mechanism that supports responsive (i.e. highly available and timely) Web services, constructed out of replicated servers. Specifically, this mechanism operates by engaging all the available replicas in supplying a fragment of the Web document that a client requires. The size of the fragment a replica is requested to supply is dynamically evaluated on the basis of the response time that replica can provide its client with. In addition, the proposed mechanism can dynamically adapt to changes in both the network and the replica servers' status, thus tolerating possible replica or communication failures that may occur at run-time. The performance results we have obtained from our experimental evaluation illustrate the adequacy of the mechanism we propose.