Corrosion of furnace wall tubes is a problem often caused by the use of corrosive fuels. The relatively high contents of lead, zinc, alkali metals and chlorides in these fuels are believed to contribute to the corrosion. Initial corrosion as a function of lead content in a wood-based fuel was studied for three materials: 16Mo3, 304L and Alloy 625. The materials were exposed for 8 h in a laboratory combustion test rig at a position resembling furnace wall conditions. The metal temperatures investigated were 350 and 400 °C. Increasing the lead content in the fuel or the temperature accelerated the corrosion rate of 16Mo3. It is proposed that lead and lead oxides in deposits react with iron chloride to form lead chloride, which when combined with alkali chlorides results in a very corrosive deposit containing low melting salt mixtures. Negligible corrosion was observed for 304L and Alloy 625.