This article studies the outage capacity of bidirectional relaying using Decode and Forward (DF) in cognitive relay networks. We consider a communication system where two sources attempt to exchange their messages through a set of cognitive relay nodes. Only relays with successful decoding and spectrum acquisition ar allowed to participate in the broadcast phase (BC). We consider two schemes for selecting the relays in the BC phase. In the first scheme, successfully decoding at least one of the two signals allows a relay to participate, while the second scheme requires successful decoding of both signals for a relay to participate. Simulation results illustrate the performance advantage of the first scheme for low SNR values. Furthermore, we use high SNR approximations in deriving closed from expressions for the outage capacity.