Recoil corrections to the Lamb shift in helium

Nuclear recoil corrections to the energies of helium S levels of order m 2 / M 5 are presented. They are shown to contribute only a small amount to the ionization energies of the 2 1 S and 2 3 S states, but to contribute significantly on the scale of accuracy of modern 4 He- 3 He isotope shift experiments.