On the basis of observations of cells (strains KB-PK and L-fibroblasts) cultivated in tissue culturesin vitrothe author believes nuclear rotation to be an active and pantypical phenomenon. He believes, however, that, with regard to the fact that the nuclei of one and the same culture do not move at the same time, in the same direction and at the same speed the inhibition of this phenomenon cannot be used as a criterion of the reaction of the cells on some noxae before it is studied more deeply. In his opinion, the rotation is in relation to the elimination of products from the nucleolus into the cytoplasm.