Improved experimental techniques are described, using a wire mesh reactor, for determining the pyrolysis yields of lignocellulosic materials. In this apparatus pyrolysis tars are rapidly swept from the hot zone of the reactor and quenched, secondary reactions are thereby greatly diminished. Particular emphasis is placed upon the measurement of the pyrolysis yields for sugar cane bagasse, an abundant agricultural waste product. The role of the important pyrolysis parameters, peak temperature and heating rate, in defining the ultimate tar yield is investigated, with the value for bagasse being 54.6% at 500 degrees C and 1000 degrees C/s. The pyrolysis yields, under similar conditions, of another biomass material, silver birch, are also reported and compared to those of bagasse.