Design and development progress is detailed. Porous support tube quality continues to improve, both through modification of extrusion equipment and through the use of pre-calcined, blended powder materials in the starting, batch material. Apparatus has been assembled and is operational to measure support tube gas diffusion and permeation coefficients. Candidate air electrode materials, having more stable physical and chemical properties, to replace tin-doped indium oxide, are being examined. Series-cell stack tests have been tested: (1) to establish the effect of variable-length cells in a stack on fuel utilization and performance, and (2) to evaluate the performance of a stack having a flame sprayed, air cathode. Results in both of these areas is very encouraging: 90% fuel utilization was obtained in the stack with variable cell length, and up to 1000 mA/cm/sup 2/ was obtained in the stack with a flame sprayed, doped lanthanum cobalt oxide cathode. The HTSOE fuel cell stack was found to be tolerant to 50 ppM H/sub 2/S in exit gas at 85% depletion (of CO/H/sub 2/ mixture), when operated at 150 mA/cm/sup 2/ for 800 h at 1000/sup 0/C. Apparatus for AC and DC bench testing of stacks under variable fuel, oxidant, temperature conditions has been constructed and is operational.