The author describes the assets and limitations of the scanning electron microscope used under routine conditions for the floristic analysis of marine micro plankton. Drawing on experience gained in the examination of Indian Ocean material collected by the R. V., ANTON BRUUN the examination of diatoms, tintinnids. radiolaria, and in particular, dinoflagellates is discussed. The considerable simplicity of the techniques involved, combined with the type of image obtained, make the instrument highly suitable for the examination of field material for taxonomical, morphological and ecological purposes. This is counterbalanced to a certain extent by the great cost of the instrument.