The endohedral nitrogen-atom-containing fullerenes, N@C-60 and N@C-70, were studied mass spectrometrically. The neutral endohedrals are thermally unstable. This instability can be followed by mass spectrometry as well as by EPR spectroscopy. The corresponding ions were studied by using mass-analyzed ion kinetic energy (MIKE) spectroscopy. Unlike metal-containing and noble-gas-containing endohedral fullerenes studied earlier, the ions N@C-60(+) and N@C-70(+) do not lose C-2 groups unimolecularly but lose the nitrogen atom instead. This indicates that the activation energy for nitrogen-atom loss is lower than that for the C-2 elimination from the cage. This was verified through the analysis of kinetic energy release distribution (KERD) measurements. The results are discussed in light of the thermal instability of nitrogen-atom-containing endohedral compounds compared to noble-gas-containing analogues.