The result for the permittivity of weakly ionized, weakly magnetized plasmas obtained by Kiss'ovski and Shivarova (1995) is analysed aiming at a description of the behaviour of low-frequency instabilities in dc discharges maintained at comparatively high gas pressures. The spectrum and the condition of instability of low-frequency drift waves arising in the discharges under conditions of comparatively high collision frequency and finite ion gyroradius are derived. (Here and are the ion gyrofrequency and gyroradius, respectively, is the ion - neutral collision frequency and R is the plasma column radius.) Results from numerical analysis are compared with experimental data previously obtained (Kiss'ovski et al 1994).