Commercial CoMo and NiMo catalysts in an oxidic and sulfided form and a gamma-alumina were deposited with pyrrole, pyridine, and quinoline. The deposited catalysts and two spent hydroprocessing catalysts were pyrolyzed and oxidized under conditions typical of regeneration of hydroprocessing catalysts. The formation of NH3 and HCN, as well as selected cases of N2O and NO, was monitored during the experiments. NH3 and HCN were formed during pyrolysis of pyrrole-deposited catalysts whereas only NH3 was formed during that of pyridine- and quinoline-deposited catalysts. For all deposited catalysts, both NH3 and HCN were formed during temperature programmed oxidation in 2% O-2. For spent catalysts, a small amount of N2O was formed in 2 and 4% O-2. For pyrrole-deposited catalysts, large yields of N2O were formed in 4% O-2. Under the same conditions, N2O yields for pyridine- and quinoline-deposited catalysts were very small.