The purpose of this topical report is to identify available information regarding the impact upon fuel cell performance of sulfur dioxide at ppM levels in oxidant gases supplied to molten carbonate fuel cells (MCFC). The general conclusions of this review are as follows: (1) The major source of sulfur dioxide in the oxidant is oxidized sulfur species coming from the fuel. (2) Sulfur dioxide in the oxidant can react with oxygen and carbonate to produce sulfate in the electrolyte. (3) Sulfate in the electrolyte is Faradaically transported to the anode where it is reduced to hydrogen sulfide. (4) The major and thus far only identifiable mechanism for performance loss in MCFC is caused by this hydrogen sulfide forming nickel sulfide on the anode. (5) There are a number of other chemical reactions in which sulfur dioxide may participate which have not been investigated. Included in this group are the oxidation to sulfur trioxide and the corrosion of nickel and nickel oxide. 14 refs., 3 figs., 2 tabs.