Wistar rats were exposed to atmospheres containing 0 (control) or 5000 ppm vinyl chloride monomer (VCM), 7 h/day, 5 days/week, for a period of 52 weeks. After 4, 13, 26 and 52 weeks each time 10 rats/sex/group were killed and subjected to extensive examinations. The present paper describes the morphological changes observed in the respiratory tract, ceruminous glands, brain, kidneys, heart and spleen. The VCM-effects included increased degree of tubular nephrosis, mild focal degeneration of the myocard, and increased haematopoietic activity in the spleen. In addition, primary tumours were found in the brain (ependymoma), lungs (papillary adenoma and mesenchymal type of tumour), ceruminous glands (mainly keratinized squamous cell carcinomas), and nasal cavity (carcinomas of the olfactory epithelium, carcino-sarcoma, esthesioneuroepithelioma). Chemicals/CAS: vinyl chloride, 75-01-4; Vinyl Chloride, 75-01-4; Vinyl Compounds