material balances for pentosan, lignin, and hexosan, during steam-explosion pretreatment of aspenwood, showed almost quantitative recovery of cellulose in the water-insoluble fraction. dilute acid impregnation resulted in more selective hydrolysis of pentosan relative to undesirable pyrolysis, and gave a more accessible substrate for enzymatic hydrolysis. thermocouple probes, located inside simulated aspenwood chips heated in 240 $degree$ c-saturated steam, showed rapid heating of air-dry wood, whereas green or impregnated wood heated slowly. small chips, 3. 2 mm in the fiber direction, whether green or air-dry gave approximately equal rates of pentosan destruction and solubilization, and similar yields of glucose and of total reducing sugars on enzymatic hydrolysis with trichoderma harzianum. partial pyrolysis, destroying one-third of the pentosan of aspenwood at atmospheric pressure by dry steam at 276 $degree$ c gave little increase in yield of reducing sugars on enzymatic hydrolysis. treatment with saturated steam at 240 $degree$ c gave essentially the same yields of glucose and of total reducing sugars, and the same yields of butanediol and ethanol on fermentation with klebsiella pneumoniae. (edited author abstract) 17 refs