Bis-to hexakisadducts of C,, (1-6) and mono-to tetrakisadducts of C,, (7-13) containing 'He atoms (endohedral helium complexes) were prepared and studied by 3He NMR spectroscopy to determine the influence of degree of functionalization and addition pattern on the chemical shift of the 'He atom. In the series of C,, derivatives, which included the previously measured 6-6 monoadduct 'He(g3C,,H,, the 3He resonance was shifted considerably upfield relative to spectral range between 6 = -11 3 4 and -12.26. The absence of further substantial upfield shifts was rationalized in terms of the compensation of deshielding due to the functionalization-induced decrease in the diamagnetic n-electron ring currents that extend around the fullerene sphere by the shielding that results from the weaker pentagonal-ring paramagnetic currents and the increased number of localized benzenoid substructures in 3-6. In conthat of 'He@jC,, (6 = -6.36) up to the bisadduct 1 (6 = -11.45). The resonances of the higher adducts 3-6, however, were shifted only slightly further up- Keywords fullerenes endohedral helium complexes -NMR spectroscopyring currents field and all appeared in a rather narrow [