Controlled ecological life support systems (CELSS) have for some years been subject to intensified studies and experiments in the U.S. and the U.S.S.R., and in Europe and Japan as well in recent years.The presently planned Space Station concepts foresee an early implementation of water and oxygen recovery in order to reduce resupply weight and volume. In view of expected increase in station and crew size the spacecraft payload limitations will require that the carbon, or food, recycling loop, the third and final part in the life support system, be closed to further reduce logistics cost. This will be practical only if advanced life support systems can be developed in which metabolic waste products are regenerated and food is produced.Dornier System has in recent years undertaken an effort to define requirements and concepts and to analyse the feasibility of a Biological Life Support System (BLSS) for space applications. Analyses of the BLSS energy-mass relation have been performed, and the possibilities to influence it to achieve advantages for the BLSS (compared with physicochemical systems) have been determined. The major problem areas which need immediate attention have been defined, and a programme for the development of BLSS has been prosed.