The conduction electron susceptibility &khgr; (q) is considered to play an important role in the magnetism of rare‐earth metals and alloys. In order to obtain information about &khgr; (q), studies of the spin waves in the alloy Tb0.76Y0.24have been carried out in a magnetic field. The magnetic structure of this alloy was found to remain spiral down to liquid helium temperature with zero field. The spin‐wave dispersion curve in this structure has already been studied along thec*‐direction, and the results were analyzed successfully in terms of a susceptibility function corresponding to a one‐dimensional system with a slight modification. In order to obtain somewhat independent information about &khgr; (q), the spin‐wave dispersion curve for the ferromagnetic phase has been studied. A field of 14 kG was necessary to transform the structure into a ferromagnet at liquid helium temperature. Spin‐wave energies which are calculated in terms of the susceptibility function determined from the measurements in the spiral structure agree rather well with the observed energies. A large damping and softening of the spin wave has been observed near the wave vectorq=0.16 which characterized the spiral configuration. The origin of the phenomenon may be related to the instability of the ferromagnetic structure.