During EASOE, 7 in situ stratospheric water vapor content measurements were performed, in the polar region, with a balloon-borne frost-point hygrometer, from November 1991 until March 1992. The comparison between the frost-point and the air temperature profiles shows on 11 December the occurrence of PSC formation conditions when a PSC was observed by lidars. Outside the vortex the mean water vapor content seems to be very stable, 4 to 5 ppmv from 16 to 25 km. But is very changeable below 16 km, due to the variability in the origin of the air masses where the measurements occur, as these air parcels come sometimes from the tropics, then bringing dry air. Inside the vortex, a vertical descent of the air masses is observed, and is estimated to be 4 km around 25 km at the end of March, before the vortex breakdown. The rehydration of the vortex induced by this descent, from February to March, is shown. ¿ American Geophysical Union 1994