Three biomass materials-coir dust (CD), wheat straw (WS), and potato pulp (PP)-were pyrolyzed under nitrogen, and the resulting chars were gasified in air at 400 degrees C. In all cases, gasification rate of the chars showed the "normal" dependence on heat treatment temperature (HTT), i.e., a decrease with increasing HTT, only up to a certain value of HTT (500, 550, and 750 degrees C for CD, WS, and PP, respectively), above which the rate dramatically increased. This contrasts with the monotonic decrease in reactivity reported for coal chars. The unusual HTT effect is suggested to be due to a change in the chemical state of the indigenous potassium species at the HTT inflection temperature.