We report lidar measurements of the aerosol content of the atmosphere for the first two months following the volcanic eruption of Mt. St. Helen. The measurements were taken near L'Aquila (Italy) with a lidar system utilizing a 50 cm diameter telescope. The measurements are compared to similar data for the previous quiescent period and show a large increase of the backscattering ratio in the stratosphere and upper troposphere. Layers have been observed at various altitudes. A strong layer at 10--14Km has been observed only initially. Layers between 14--25Km have been observed continually. These features show a considerable day to day variability.