The concurrency control of transactions in a real-time database must satisfy not only the consistency constraints of the database but also the timing constraints of individual transactions. In this paper, we present a real-time concurrency control protocol that can be used in a distributed and decomposable real-time database. The protocol is based on the integration of a modular concurrency control theory with a real-time scheduling protocol called the priority ceiling protocol. This protocol supports the replication of data objects and avoids the formation of deadlocks. Finally, an analysis of the performance of this protocol is presented.