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Caching is a key technique for improving the data retrieval performance of mobile clients in mobile environments. The emergence of robust and reliable peer-to-peer (P2P) technologies now brings to reality what we call "cooperative caching " in which mobile clients can access data items from the cache in their neighboring peers. We discuss cooperative caching in mobile environments and proposes a cooperative caching scheme for mobile systems, called COCA. In COCA, we identify two types of mobile clients: low activity and high activity. They are referred to as low activity mobile client/host (LAM) and high activity mobile client/host (HAM) respectively. Both LAM and HAM can share their cache. The server replicates appropriate data items to LAMs so that HAMs can take advantages of the LAM replicas. The performance of pure COCA and COCA with the data replication scheme is evaluated through a number of simulated experiments which show that COCA significantly reduces both the server workload in terms of number of requests and the access miss ratio when the MHs reside outside of the service area. The COCA with the data replication scheme can improve the overall system performance in other aspects as well.