In summer 1985, the United States Nuclear Regulatory Commission (USNRC) published an interim report about the state of the work done for a more realistic description of the activity source terms that can be initiated by major accidents in light water reactors. It presents an overview of the present status of research work on this topic, especially in the USA. The statements contained in the report are of some interest also to the Federal Republic of Germany. They could affect Phase B of the German Risk Study.