The electron density relative variability at fixed heights is studied using electron density profiles obtained from two Argentine ground ionosondes measurements. For midnight conditions, the results show that, in general, the variability increases with height reaching a maximum below the peak density. The highest variability was observed at 280 km of height for night equinox and high solar activity. Variability is considerably larger during night than during daytime at F region altitudes. An opposite but much smaller difference is seen al E region heights. At noon variability is larger at low solar activity than at high solar activity because of the smaller mean values.