In a mobile dabase system, caching at a mobile host could conserve the limited wireless bandwidth while reducing the query response time, and yet cache consistency needs to be maintained. The basic cache consistency scheme is for the server to periodically broadcast an invalidation report that identi.es the updated data objects so that the mobile hosts may purge the stale data objects from their caches. In case that long period of disconnection prevents a reconnecting mobile host from guaranteeing validity of its cache based solely on the invalidation report received, the mobile host could request the server to check validity of its cache. In this paper, we propose a set of new cache validation schemes that can efficiently conserve the bandwidth both in cache validation and query processing afterwards. The performance of our schemes is evaluated through the detailed simulation experiments.