The stratospheric aerosol layer between 15 and 25 km altitude is an important factor in the balance of the global radiation budget. The eruption of the Mount St. Helens in Washington, USA, on 18 May 1980 violated the quasi stationary situation in the stratosphere which was established after the decay of the post-Fuego aerosol during the years 1974 to 1976. At tropopause level the cloud was observed over the east coast of the US and Canada on 21 May 1980. The further transport over the Atlantic was estimated by first guess trajectory constructions. The arrival of the eruption cloud over Europe was observed by the authors employing in situ techniques and remote sensing. The in situ measurements of atmospheric SO2 were performed during an aircraft ascent up to 13.7 km on 26 May 1980 over southern Scandinavia. In contrast to an aircraft ascent over southern Germany on 24 May 1980 a tenfold increase in SO2 mixing ratio at tropopause level was observed. Remote sensing by ground based ruby lidar at Garmisch-Partenkirchen (47.5 ¿N, 11 ¿E) from 25 May to 29 May 80 indicates an aerosol peak at a height of 11 to 12 km, which was initially coupled to the tropopause, but later clearly separated from that level.