A new balloon borne instrument called a backscattersonde has been used to study Polar Stratospheric Clouds (PSCs) at Alert, NWT (82 ¿N, 61.5 ¿W) during January and February of 1989. These measurements were supplemented with frost point, ozone and nitric acid vapor soundings. Type I PSCs were observed at temperatures and pressures generally consistent with present vapor pressure models of HNO3/H2O condensate, but some noticeable inconsistencies exist. It is suggested that these apparent problems, as well as some characteristic peculiarities in the PSC profiles, could be explained by the presence of two phases of the HNO2/H2O condensate. ¿ American Geophysical Union 1989