The relaxation of the fibre-on-plate geometry was studied experimentally using glass. Various fibre diameters and temperature/time schedules were used. Excellent agreement with the theoretical predictions of Hopper was obtained. The determination of the surface tension of glass at low temperature by this method is discussed. A value of 0.19 N m(-1) at 600 degrees C was measured for a modified Na-K-Ba-Sr-silica glass, which differs significantly from the sessile-drop value of 0.35 N m(-1), extrapolated from high-temperature data. Influencing factors are discussed. The difference is probably due to the presence of water vapour which considerably lowers the surface tension of glass at low temperature.