We describe here the performance and the use of microtechnology in a miniaturized bioreactor developed for the continuous cultivation of yeast cells, Saccharomyces cerevisiae, in microgravity. This bioreactor has been used on two Shuttle missions, where its functionality was successfully demonstrated. In the future, bioreactors will become a key element for long-term experiments, and would also be applied in the cultivation of mammalian cells or tissues for medical applications. (C) 2000 Elsevier Science Inc. All rights reserved.