Stratosperic sulfuric acid vapour concentrations have been measured in the altitude region from 23.5 to 33 km by the passive chemoionisation mass spectrometry method (PACIMS), in recent years sucessfully introduced by our group for stratosperic trace gas detection. The data agree with current model predictions at most heights. Implications of the present data for the stratosperic sulphur cycle, stratoperic aerosols, and stratosperic ions are discussed.