The performance of currently available minibioreactors with volumes below about 100 ml is reviewed. Bioreactors are characterized by their area of application, by mass transfer and mixing characteristics and by their suitability for on-linemonitoring and control. The review comprises shaken bioreactors such as shake-flasks, microtiter plates and test-tubes, stirred bioreactors including spinner-flasks for the cultivation of mammalian cells and various special reactors particularly involving on-line monitoring as e. g. membrane inlet mass spectrometry and NMR.