This paper presents a new cooperative MAC (Medium Access Control) protocol for IEEE 802.11-based mesh networks. The protocol is characterized by two features: on-demand relaying and selection of the best relay terminal. ”On-demand relaying” means that a cooperative communication occurs only when a destination terminal fails in decoding the data transmitted by a source terminal. This approach allows minimization of bandwidth degradation due to both cooperation implementation and cooperative communications. ”Selection of the best relay terminal” means that a relay selection is implemented when cooperation is needed. This feature allows maximization of the spatial diversity order. The outage probability of the new protocol is compared to the outage probability of other cooperative MAC protocols.