AbstractThe influence of drugs on the shape and the size of nuclear bodies ofEscherichia colihas been studied by electronmicroscopy and sedimentation experiments. Antibiotics inhibiting protein synthesis but not RNA synthesis decrease the size of the nuclear body. Inhibition of RNA synthesis brings about a disintegration of the compact structure of the nucleoid. From electronmicrographs it can be seen that most drugs cause a condensation of the nucleoplasm into one single coherent region. Inhibition of DNA synthesis does not have much influence on the shape of the nuclear body. It is concluded that mainly the transcription process affects the form of the nuclear body.