The long-term properties of Ni/yttria stabilized zirconia (YSZ) cermet anodes for solid oxide fuel cells were evaluated experimentally. A total of 13 anodes of three types based on two commercial NiO powders were examined. The durability was evaluated at temperatures of 850 C-degrees, 1000 C-degrees and 1050 C-degrees over 1300 to 2000 h at an anodic d.c. load of 300 mA cm(-2) in hydrogen with 1 to 3% water. The anode-related polarization resistance, R-P, was measured by impedance spectroscopy and found to be in the range of 0.05 to 0.7 Omega cm(2). After an initial stabilization period of up to 300 h, R-P varied linearly with time within the experimental uncertainty. At 1050 C-degrees no degradation was observed. At 1000 C-degrees a degradation rate of 10 m Omega cm(2) per 1000 h was found. The degradation rate was possibly higher at 850 C-degrees. A single anode was exposed to nine thermal cycles from 1000 to below 100 C-degrees at 100 C-degrees h(-1). An increase in R-P of about 30 m Omega cm(2) was observed over the first two cycles. For the following thermal cycles R-P was stable within the experimental uncertainty.