Data are presented on the consumption of duff by fire on six plots in a jack pine (PinusbanksianaL.) stand and six plots in a red and white pine (P.resinosaAit andP.strobusL.) stand. The amount consumed was found to correlate well with the moisture content of the duff before fire, and with the Duff Moisture Code, a component of the Canadian Forest Weather Index. A tentative theory to account for the amount of duff consumed is presented in terms of (a) downward heat transfer within the flaming front, and (b) the energy required to heat the duff to ignition temperature.