In this paper, the (first) results of a systematic comparison of the influence of the heating regimes on the pyrolysis of biomasses are presented. Flash and fast pyrolysis regimes as those encountered in the industry are reproduced. The more severe the heating regime the larger the amount of syngas produced and the smaller the amount of solid residues and tar. Cellulose pyrolyses much better than lignin. At high temperature and in flash pyrolysis, there is no evidence of tar production. The specific volume of syngas produced can be above 1 Nm3 /kg.