Wireless Medium Access Control (MAC) protocols such as IEEE 802.11 use distributed contention resolution mechanisms for sharing the wireless channel. In this environment, selfish hosts that fail to adhere to the MAC protocol may obtain an unfair share of the channel bandwidth. For example, IEEE 802.11 requires nodes competing for access to the channel to wait for a "backoff" interval, randomly selected from a specified range, before initiating a transmission. Selfish nodes may wait for smaller backoff intervals than well-behaved nodes, thereby obtaining an unfair advantage. We present modi.cations to the IEEE 802.11 protocol to simplify detection of such selfish hosts. We also present a correction scheme for penalizing selfish misbehavior. Simulation results indicate that our detection and correction schemes are successful in handling MAC layer misbehavior.