It is shown that enzymatic hydrolysis of biomass can decisively contribute to supplement indigenous sources of fuels and chemicals. The utilization of hemicellulose and cellulose requires preliminary pretreatment of biomass which can be efficiently accomplished and references are given for the optimization of recovery procedures. Bioconversion of both hemicellulose and cellulose is discussed and the effects of temperature, pH, substrate concentration and product inhibition are shown on the basis of experimental evidence. Process by-products-low molecular weight chemicals formed during biomass pretreatment - were fully characterized and details are reported of the analytical methods which were employed. It was found that higher sugar yields are reached when hydrolysis is performed making use of enzymic composites from different strains.