The oscillating-sphere method has been applied to find the viscosities of liquid lithium, rubidium and caesium from the neighbourhood of the melting-point upwards over a range of temperatures. For lithium it was necessary to construct a nickel-lined metal sphere, as liquid lithium attacks glass and many metals. This involves certain technical difficulties, which have been overcome. The peculiarities of the three metals made necessary the elaboration of special methods of handling. Measurements for sodium and potassium having been already made, the viscosities of all the alkali metals are now available. The results, as regards both the absolute values of the melting-point viscosities and the variation of viscosity with temperature, accord well with the simple theory put forward by one of the authors some years ago. The values for the characteristic temperature which can on this theory be derived from the melting-point viscosities agree well with the values derived from the specific heats for the first three metals, and are calculated for rubidium and caesium, for which values derived from other sources are not available.