The film shows the cytopathic changes of human epithelial cells and of epithelia of monkey kidneys in tissue culture after infection with poliomyelitis virus type 1. Under the influence of the infection certain cellular cytoplasm components are at first displaced into the region surrounding the cell nucleus, and a hyaloplasm is formed. Then pyknosis and dissociation of the cytoplasm occur with formation of a branched reticulum of fine cytoplasm filaments, which stick for some time to the bottom of the culture vessel. The stimulation of cell division observed in the cells infected with poliomyelitis virus is shown. After division the daughter cells show the cytopathic effect characteristic for this type of virus.