With Spacelab approaching its operational stage, ESA has initiated the Follow-On Development Programme. The future evolution of Spacelab elements in a continued U.S./European cooperation is obviously linked to the U.S. STS evolution and leads from the sortie mode improvements (Initial Step) towards pallet systems and module applications in unmanned and manned space platforms (Medium and Far Term Alternatives). The main design driver for the life support system in the Initial Step is the extended mission duration (20 days). This improvement will make Spacelab compatible with the Shuttle EDO.The Medium and Far Term Alternatives are oriented around the Science and Applications Manned Space Platform and the Space Operations Center considering Spacelab module applications for future manned space platforms. The preliminary definition of the design on subsystem level for regenerative life support systems with various degree of closure has been completed in early 1982.