The molten carbonate fuel cells (MCFC), as an alternative power source, present one of the most promising and environmental cleanest processes. As a high temperature fuel cell, problems arise due to corrosion of the metallic current collectors and voltage drop by formation of insulating corrosion products. The aim of this work is to develop Fe-Cr stainless steels, alloyed with different amounts of Mn, Co, Si, Ni, Mo, in order to obtain an acceptable thin corrosion scale with a low electrical resistivity by spinel formation. The formation of spinel layers as corrosion products, containing multivalent elements like Mn, Co and Mo is expected to give satisfactory results. In situ conductivity measurements and corrosion tests have been performed in the presence of a (Li, K) carbonate melt at 650 degreesC under an oxidizing gas atmosphere (15 vol.% CO2 and synthetic air) up to 5000 h. Investigations of the corrosion scales on the hot rolled alloys indicated a solubility of Co and Mn in the spinel layer, formed under the simulated MCFC conditions. Outward diffusion of Mn and Co was observed after longer reaction times. An inner oxidation zone was also measured and connection between conductivity behaviour and the composition of this layers is found. (C) 2004 Elsevier B.V. All rights reserved.