A Pt/ZrO2 catalyst has been investigated by temperature-programmed reduction and temperature-programmed desorption of hydrogen. Hydrogen spills over from Pt onto the ZrO2 surface at about 550 degrees C. One part of spillover hydrogen is consumed by a partial reduction of zirconia. The other part is adsorbed on the surface and is desorbed at about 650 degrees C. This desorption is a reversible one, i.e. it can be followed by a renewed uptake of spillover hydrogen. No connection between dehydroxylable OH groups and spillover hydrogen adsorption has been observed. The adsorption sites for the reversibly bound spillover hydrogen were possibly formed during the reducing hydrogen treatment.