The formation of C-60 dimers with a nitrogen atom in one of the C-60 cages is studied. The dimers are produced by ball milling of a mixture of N@C-60 With C-60 and a suitable additive. The products are purified by high pressure liquid chromatography (HPLC) and identified by UV/Vis and IR spectroscopy. Electron paramagnetic resonance (EPR) measurements show that nitrogen remains in C60 during the dimerization and keeps its atomic configuration. A slight deformation of the electron shell reflecting the distortion of the cage is observed. The optimization of the dimer formation is described.