Biomass is gaining increasing importance as a renewable energy source for the production of heat, electricity and transport fuels. However, corrosion issues are numerous and include accelerated wastage under ash and alkali salt deposits, erosion, and metal dusting in conjunction with gasification. This work focuses on deposit issues and is based on laboratory exposures for a total of 960 hours at 550°C (1022°F) and 700°C (1292°F) under deposits of 52.4 wt% KCl + 47.6 wt% K2SO4 in a nitrogen- based gaseous atmosphere containing 15% H2O, 5%O2, 13%CO 2 and 0.02%HCl. The materials tested include carbon steel, low alloyed steels with 2%Cr or 9%Cr, the austenitic AISI 304 and the high temperature grade 253MA (21%Cr, 11 %Ni, 1.6%Si, Ce). Metal loss data obtained from metallographic evaluation show the corrosion rate to decrease in this order and illustrate how materials substitution can permit an increase in process temperature. Examination of the reaction interface underlines the importance of both chlorination and oxidation in the materials corrosion process. © 2009 by NACE International.