The inherently distributed nature of wireless sensor networks (WSN) applications makes clear the necessity of adopting middleware systems in their development. However, the middleware must be designed regarding proper characteristics of WSNs such as low power consumption, processing capacity and bandwidth. In this scenario, we propose a middleware (TS-Mid) that provides communication based on a JavaSpace-compliant tuple space (shared memory), whilst it enables the creation of logical regions inside WSNs. The communication through tuple space is interesting in wireless networks and the notion of logical regions serves as a basic mechanism for power saving.