In this paper we study opportunistic communication in two relay channels, the shared relay channel (SRC) and the X-relay channel (XRC). The shared relay channel consists of multiple non-interfering source-destination pairs sharing one relay. The X relay channel is a multi-source multidestination network where each source has a message for each destination and the network is assisted by one relay. The diversity multiplexing tradeoff is calculated for these two networks under protocols including non-orthogonal amplify-forward, dynamic decode-forward, and compress-forward. The performance of simpler protocols can be easily deduced from the results in this paper.