Measurements of gaseous sulfuric acid and sulfur dioxide were made in the winter arctic troposphere and lower stratosphere, using aircraft-borne mass spectrometers. The measurements, covering altitudes between 3.5 and 11.4 km, took place on 14 and 18 February, 1987 in Northern Scandinavia. The abundance of H2SO4 was around 0.01 to 0.06 pptv (parts per trillion by volume) and the measured SO2 volume mixing ratios are around 50 to 400 pptv in the troposphere and decrease steeply above the tropopause to about 10 pptv. This decrease above the tropopause is in contrast to previous measurements showing constant or even increasing SO2 mixing ratios. The combined H2SO4 and SO2 measurements offer an interesting opportunity to infer hydroxyl radical concentrations. Inferred OH concentrations are around 0.1--1.0¿105 cm-3 being roughly consistent with model predictions for winter time high latitudes. ¿ American Geophysical Union 1992