Extensive field experiments were performed in April/May 1992 and October/November 1993 in order to investigate the aerosol-cloud relationship at the high-alpine site Jungfraujoch, 3450 m asl. Aerosol and cloudwater samples were collected simultaneously and analyzed for the major water- soluble anions and cations. In addition, the cloud liquid water content (LWC) and the aerosol size distribution were measured. A nearly complete activation of particles with diameter d ≥ 0.2 μm was observed, independent of the number concentration. Since there was only a slight variability of the LWC, it was concluded that higher aerosol concentrations at high-alpine sites are associated with smaller droplet sizes. Long-term measurements of LWC and of the aerosol concentration suggested that this may be true throughout the year, giving additional evidence for a possible impact of anthropogenic aerosols on cloud albedo.