Deuterium NMR line shapes of carbon black (N220) filled cis-1,4-poly(butadiene) networks have been examined. The effect of the susceptibility of the filler on the NMR line shape has been considered. The theory proposed by Brereton and Ries for deuterium NMR line splitting in spectra of polymer networks was used to fit the experimental data. It was found that the polymer segments near the surface of a filler particle experience a different local magnetic field from the remaining segments, due to the susceptibility of the carbon black. This effect gives rise to an asymmetry in the NMR spectrum, which until now has not been explained. Additionally, this analysis determines the fraction of polymer units affected by the local field of the filler particles and provides information about the effect of the macroscopic deformation on these attached chains.