In order to elucidate possible reaction paths to the formation of P-N bonds in interstellar space and to provide data for the interpretation of recent experiments, the reaction of P+ ((3)p) with methylamine has been investigated. In particular, the G2(MP2) methodology has been applied to the triplet potential energy surface of [H-5, C, N, P](+). Numerous minima on this surface have been found, and transition state structures connecting those which lie along important reaction paths have been determined. The global minimum on the PES is the ion-molecule complex P+ NH2CH3, which lies 95.7 kcal/mol below the separated reactants. Barrier-free reaction paths leading to (PNH2+ + CH3), (PH + CH2NH2+), and atomic and molecular hydrogen abstraction have been found. In agreement with experimental results, these first two reactions appear to be favored.