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Smart antennas present a radical way to improve the capacity of wireless networks. The advantages of such antennas can be leveraged by the MAC and higher layers. In this paper, we present SPACE-MAC, a MAC protocol which enables "spatial reuse" of the medium by multiple transmit/receive pairs which are in the same collision domain. SPACE-MAC prevents interference between such pairs by selectively ing the signals from potentially interfering transmissions. This is achieved in a totally distributed fashion utilizing channel state information (CSI) at both transmitter and receiver to adjust antennas weights for each packet transmission. SPACE-MAC can operate effectively in cluttered (e.g., indoor) environments. SPACE-MAC achieves spatial reuse without requiring a separate channel for exchanging channel state information. This allows considerably better channel utilization. We investigate performance improvements of SPACE-MAC with respect to IEEE 802.11 DCF MAC using omnidirectional antennas.