If man leaves Earth for a long time to settlements on the Moon or Mars, he will be dependent of Closed Ecological Life Support Systems (CELSS) for the recycling of waste and the production of food. A large amount of the inedible plant material has to be pretreated and converted into a form which can be recycled. The main portion of this biomass is lignocellulosic material which cannot or only slightly be degraded by micro-organisms. White-rot fungi like Pleurotus spp. (oyster mushroom) or Lentinus edodes (shiitake or black Chinese mushroom) degrade these fibrous material more efficient than other micro-organisms and produce edible and also tasteful mushrooms which will increase the quality and nutritional value of the settlers diet.In the MELISSA (Micro-Ecological Life Support Alternative) project, a project under the management of ESA to study CELLS, it was observed that also human faeces contain a considerable amount of fibrous materials which pile in the loop. Because also higher plants are part of the MELISSA cycle, it has been decided to study the use of white-rot fungi for the breakdown of the lignocellulotic material.In this paper the outcome of a feasibility study on these fungi in CELLS, especially the MELISSA cycle, will be reported. This project is performed in the Netherlands by the Agrotechnological Research Institute (ATO) and Stork Product Engineering (SPE).