Wireless Body Area Networks (BAN) are supposed to operate in very low transmit power regime in order to keep the Specific Absorption Rate (SAR) low. Low power transmissions are known to be very error prone. However, high reliability of communications is needed for several healthcare applications. It has been observed that the fluctuations of the Received Signal Strength (RSS) at the nodes of a BAN on a moving person show certain regularities and that the magnitude of these fluctuations are significant (5 – 20 dB). In this paper, we present BANMAC, a medium access control (MAC) protocol based on cross-layer design approach where medium access decisions are tightly integrated with physical layer conditions. BANMAC monitors and predicts the channel fluctuations and schedules transmissions opportunistically when the RSS is likely to be higher. We report the design and implementation details of BANMAC integrated with the IEEE 802.15.4 protocol stack. We present experimental data which show that the packet loss rate (PLR) of BANMAC is significantly lower as compared to that of the IEEE 802.15.4 MAC. For comparable PLR, the energy consumption of BANMAC is also significantly lower than that of the IEEE 802.15.4 MAC. © 2016