The ultrastructure of the Euglena gracilis nucleus has been studied with electron microscopy and prefential staining of ribonucleoproteins. The interphase nucleus chromatin is mainly concentrated in chromonemata - i.e. elongated threads of condensed chromatin. Part of them is directed to the nuclear envelope, with which they are in contact. The number of these contacts is approximately equal to the chromosome number. The Euglena gracilis nucleoplasm is rich in various RNP-components, which points to the transcriptional activity of chromatin, although the majority of chromatin is condensed.