In this paper, we propose a novel retransmission scheme that can substantially increase the throughput of wireless local area networks (WLANs). The main idea of the scheme is to enable cooperative communication in the medium access control (MAC) layer such that one node can retransmit messages for its neighboring nodes if the delivery of those messages failed previously due to transmission error. In addition, we also redesign the transmission and acknowledgement policy of the existing IEEE 802.11 protocol in that 1) an upper layer packet will be partitioned into blocks, and 2) the receiver of a message can acknowledge individual blocks through negative acknowledgement (NACK). To evaluate the performance of the proposed scheme, we conduct extensive simulation study under various conditions, such as number of nodes, size of packet, and bit error rate. Simulation results show that, the proposed scheme can significantly increase the throughput performance of WLANs under these conditions, and an optimal block size can lead to the highest throughput in each specific scenario.