Euglena gracilis, a unicellular photosynthetic flagellate, serves as a model system in signal transduction research. To further study its complex gravitaxis, experiments under microgravity are desirable. In preparation for long-term experiments on a space station, an autonomous cultivation unit has been developed and the culture conditions and surveillance methods have been established. The running time of more than 600 d under closed conditions with light as the only source of energy confirmed the stability of the Euglena population and gave new insights into its behavior. Physicochemical parameters such as oxygen concentration, temperature and pH as well as physiological parameters including cell density, motility, gravitactic orientation and pigmentation were recorded on a frequent basis. The suitability of the botanical bioreaction to serve as an oxygen supplier for animals in a closed system was demonstrated.