A novel microscale test method was developed for testing catalysts. A pyrolyser connected to a gas chromatograph was used for pyrolysing the biomass sample and for leading the pyrolysis vapours through the catalyst for instant analysis. The injection port of the gas chromatograph was used as a fixed-bed catalyst reactor. Detection of reaction products was carried out with an atomic emission detector to quantify the various elements or with a mass selective detector to identify the compounds. The test method was applied to treating pyrolysis vapours of Scots pine sawdust with ZnO, MgO, dolomite and limestone. Mass balances for carbon and hydrogen were determined with and without the catalyst. The carbon yields in liquid fraction decreased with all the catalysts studied. The highest yields were obtained with ZnO. Product distribution in pyrolysis vapours was rather similar with ZnO or without any catalyst. With MgO, dolomite and limestone, the compounds of pyrolysis vapours comprised mainly gases, water and degradation products of polysaccharides as well as some aromatic hydrocarbons.