The current driven ion acoustic instability has been studied in a quiescent magnetized argon plasma for electron densities in the range from 1010to 1011cm−3, an electron temperatureTeof 2.2 eV, an electron‐ion temperature ratioTe/Tiof 15, a homogeneous magnetic field of 400 G, and neutral gas pressures in the range from 1×10−3to 5×10−3mm Hg. Coulomb collisions are important for these experimental conditions. The instability occurs for dc currents in the range from 100 to 600 mA. The saturation appears to be explained by electron trapping. The nature of the instability is identified from measurements of the cross power density spectrum and the characteristic parameters like electron drift velocity, collisional damping, electron temperature, and electron‐ion temperature ratio are determined precisely from an observation of low frequency ion acoustic test waves using an unperturbative method of microwave interometry.