A rocket-borne optical hygrometer for night time in situ measurements of the middle atmospheric water content was successfully launched from Esrange, Sweden, in December 1994. Utilizing the OH photofragment fluorescence technique, the instrument takes measurements in an undisturbed volume outside the rocket shock front. A profile of water vapor was obtained between 17 and 70 km. The stratospheric mixing ratio increases from 3.5 ppmv near 20 km to around 6 ppmv above 45 km, while the mesospheric profile shows a strongly stratified structure. The results are discussed in terms of horizontal transport and compared to recently published model results on the redistribution of water vapor in the winter polar mesosphere. ¿ American Geophysical Union 1996