Normal stress effects arising in the torsional motion of a cylindrical mass of polyisobutylene solution are measured. The precautions which must be taken in making the measurements and the corrections which must be applied to them in order that the results may be compared with theory are discussed in some detail. The distribution of normal stresses over the plane ends of the cylindrical mass and the dependence of this on the experimental conditions is shown to be consistent with the phenomenological theory advanced by Rivlin (1948a). From the normal stress measurements, the normal stress coefficient, defined in this theory, is evaluated and the manner in which it depends on velocity gradient is found. Finally, the dependence of the normal stress coefficient on solution concentration and temperature is investigated.