In most planar solid oxide fuel cell (SOFC) stack designs, the interconnect, which is typically made from a ferritic stainless steel (SS), is hermetically sealed to the ceramic positive electrode-electrolyte-negative electrode by a sealing glass. To maintain the structural stability and minimize degradation of the stack performance, the sealing glass must be chemically compatible with the SS interconnect. In this study, a barium-calcium-aluminosilicate (BCAS)-based glass ceramic, specifically developed as a sealant in SOFC stacks, and a ferritic SS (AISI446) were selected as examples to increase the understanding of the chemical compatibility issues in SOFCs. Evaluation of the interfaces of coupon joints indicated that interactions between the BCAS glass ceramic and the ferritic SS were dependent on the exposure conditions. At the edges of joints, where oxygen or air was accessible, the interaction often led to the formation of BaCrO4, while in the interior of the joints, chromium or chromia dissolved into the glass to form a thin layer of chromium-rich solid solution. It was also found that, in the interior of the joints, the interaction often resulted in the formation of pores aligned along the interface. It appears the pore formation along the interface can be avoided through a preheat treatment. (C) 2003 The Electrochemical Society.