It is experimentally known that with increasing pressure and current the positive column of the glow discharge constricts. A qualitative discussion of the electron particle balance displays certain requirements for the effective diffusion coefficient Deff and the production coefficient αeff of the electrons With increasing distance from the axis either the diffusion coefficient Deff should increase or the production term αeff should decrease down to negative values. We discuss to which extent the Various physical proceses can meet these requirements. The constriction caused by the presence of negative ions is evaluated from the transport equations. From the solution of our eigenvalue problem we have the radial electron density distribution and the electric field as functions of the current, pressure and radius.