Hydrogen evolution from 0.5 M H2SO4 on Ti electrodes coated with a RuxTi1-xO2 (x = 0.04-0.5) layer has been studied by potentiostatic polarisation, cyclic voltammetry and ac-impedance spectroscopy. The results indicate that after a certain activation period the performance of such an electrode coating is comparable to platinum. The addition of small amounts of sodium molybdate increased the capacitance of the electrode and a reduction of the performance was observed. Increasing the temperature of the pure electrolyte from 20 to 75 degreesC caused an increase in the rate of the hydrogen evolution and in addition an increase of the electrode capacitance. The electrodes have been found to be rather tolerant to chloride and Fe 21 ions, and could hence be promising candidates as catalyst materials for solid polymer water electrolysis systems. From steady state measurements the Tafel slopes were found to change from - 105 mV/decade for pure titanium to about - 40 mV/decade for the (Ru-Ti)O-2 coated electrodes. The exchange current densities were calculated from the steady state curves, as well as from impedance data. to be about 10(-4) A cm(-2) after activation.