Hard amorphous hydrogenated carbon-nitrogen films were obtained by PECVD of pure methylamine and methylamine-acetylene mixtures. The chemical composition of the films was determined by nuclear techniques, and their structure examined by infrared and Raman spectroscopies. The film obtained from pure methylamine have a NC atomic ratio of 0.64, and a Raman spectrum that is characteristic of nanocrystalline graphitic carbon films. The films obtained from acetylene-methylamine mixtures show the same dependence of the structure details on the nitrogen content as already observed in a-C(N):H films deposited using other gas mixtures, i.e. a progressive increase in sp2 character of the carbon atoms when the nitrogen content in the film increases.