For periods of time ranging from 22 seconds in parabolic flights and up to two weeks on sattilites, human cells were exposed to real or simulated weightlessness on a Random Positioning Machine and a 2D clinostat and analysed afterwards. By this approach we can increase our knowledge regarding health problems of space travellers and in parallel we get new information concerning several diseases of humans on Earth. Surprisingly, we also observed that single cells exposed to simulated microgravity assemble to three-dimensional aggregates resembling the tissues from which these cells are originating. Such aggregates can already be used to study molecular mechanisms involved in angiogenesis or cancer cell apoptosis sparing animal experiments. In the future, we will see whether they can be additionally used for medical transplantation.