Rice husks were pyrolysed in a fluidised bed reactor at 400, 450, 500, 550 and 600 degrees C. The rice husks were then pyrolysed at 550 degrees C with zeolite ZSM-5 catalyst upgrading of the pyrolysis vapours at catalyst temperatures of 400, 450, 500, 550, and 600 degrees C. The pyrolysis oils were collected in a series of condensers and cold traps and analysed to determine their yield and composition in relation to process conditions. The gases were analysed off-line by packed column gas chromatography. The pyrolysis oils before catalysis were homogeneous, of low viscosity and highly oxygenated. Polycyclic aromatic hydrocarbons (PAH) were present in the oils at low concentration and increased in concentration with increasing temperature of pyrolysis. Oxygenated compounds in the oils consisted mainly of phenols; cresols, benzenediols and guaiacol and their alkylated derivatives. In the presence of the catalyst the yield of oil was markedly reduced, although the oxygen content of the oil was reduced with the formation of coke on the catalyst. The influence of the catalyst was to convert the oxygen in the pyrolysis oil to largely H2O at the lower catalyst temperatures and to largely CO and CO2 at the higher catalyst temperatures. The molecular weight distribution of the oils was decreased after catalysis and further decreased with increasing temperature of catalysis. The catalysed oils were markedly increased in single ring and PAH compared to uncatalysed biomass pyrolysis oils. The concentration of aromatic and polycyclic aromatic species increased with increasing catalyst temperature. (C) 2000 Elsevier Science Ltd. All rights reserved.