The first test flight of a new balloon-borne ACIMS (Active Chemical Ionisation Mass Spectrometry) instrument devloped at our laboratory was successful and provided a wealth of new and interesting information on stratospheric trace gases. In the present paper, a brief discussion of the experimental method is given and trace gas abundances of acetonitrile (CH3CN), acetone ((CH3)3CO), and nitric acid (HNO3) are presented. ¿ American Geophysical Union 1987