Several WLAN standards, such as Hiperlan-2, have chosen OFDM as a transmission technique due to its multipath performance. However, in these standards spectrum is not optimized. This paper analyzes the performance of single-user and multi-user constant-energy bit loading in Hiperlan channels. We show that bit rates may be increased up to 12 times in the single-user case and a gain of more than 100% may be achieved relative to Hiperlan-2 in multi-user scenarios.