[en] Since the founding of the Institute, a reorientation of the scientific direction was initiated: From the production and application of radioisotopes during the period before 1992 toward the new focus of radioecological research for risk assessment and remediation of radionuclide contaminations. The research relates to contamination problems from uranium mining in the German states of Saxony and Thuringia and in the neighboring Czech Republic, and from nuclear weapons production, testing, and accidents in the former Soviet Union. The new research direction of the Institute covers the essential aspects of radionuclide transport in the geo- and biosphere. It includes the distribution of radioactivity in ground- and surface waters and in air. We are studying the interaction of radioactive materials (a) at the interface between aqueous phase and rocks, minerals and soils, (b) the formation and distribution of colloids and aerosols, and (c) the mobilization and retardation of radionuclides through the interaction with organic contaminants and biological decay products. Our studies are essential for the successful development of environmental decontamination and remediation strategies. This report reflects the scientific transition of the Institute. The contributions to the section on ''Ecological Research'' are already focused toward the new challenge. The research that is summarized as ''General Research'' and ''Chemistry of the Heavy Elements'' clearly bear the elements of aerosol science. (orig.)