The anodic stability of an electrodeposited ruthenium electrode was measured by anodic galvanostatic polarization in 0.5 mol dm(-3) H2SO4 solution. The role of water and adsorbed hydroxyl groups in electrode stability was determined by means of thermogravimetric analysis. A continuous weight loss due to water removal and condensation of hydroxyl groups was detected between 120 and 430 degrees C. The loss of a hydrous component of the oxide layer was in direct correlation with the increase of the anodic stability. Between 430 and 480 degrees C a weight gain was detected on the thermogravimetric curve. It was attributed to the formation of the ruthenium oxide layer in a higher oxidative state. This finding was confirmed by X-ray photoelectron spectroscopy measurements.