The Vlasov–Maxwell equations are used to investigate the stability of azimuthally symmetric perturbations (e.g., sausage and hollowing modes) of an electron or ion beam immersed in a resistive plasma. The perturbed space charge and plasma current are treated self‐consistently for any value of the plasma conductivity. A similar analysis of the hose instability is also carried out. It is assumed that &ngr;/&ggr;b≪1, where &ngr; is Budker’s parameters and &ggr;bmc2is the characteristic beam electron energy. The analysis is carried out for the ’’loss‐cone’’ distribution function in which all of the beam electrons have the same value of energy (in a frame of reference rotating with angular velocity &ohgr;b) and the same value of axial canonical momentum. In the high conductivity regime, the system is shown to be strongly destabilized by a sufficiently large value of the fractional current neutralization.