Diatom samples collected from natural habitats contain usually with both alive and dead cells. Comparisons of the data obtained from the parmanent slides made with stained materials and with cleaned materials indicated significant difference with regard to community structure, i. e. total number of species and relative frequency of species. The difference was marked in the case of the sample contained many dead cells and almost of them were allochthonous in origin. Parmanent slides of cleaned materials have no information about the state of cells at the time of sampling and therefore the data obtained from the slides will lead us to erroneous conclusion. In the parmanent slides made with the materials which stained with Mayer's Hematoxylin and mounted with Pleurax mounting medium, alive and dead cells can be distinguished and thereby the data obtained from the slides will lead us to correct conclusion.
