Author performed intraoperative cytology of 236 pneumomediastinal processes, 251 mammary and 45 other focal lesions. He used fine needle asperation or scraping of pathological tissue and hematoxylin-eosin staining of smears. Diagnosis of pulmomediastinal processes was reliable in carcinomas, chondrohartomas, and polymorphocellular sarcomas. Unreliability as to biological behaviour was found in identification of low grade malignant mesenchymal tumours which needed histology. Cytokeratin expression verified the diagnosis of thymoma from routine staining and enabled cytological and histological identification of extensive bronchioloalveolar epithelial hyperplasia associated with specific and unspecific inflammations or marginally with primary as well as secondary epithelial and mesenchymal malignant tumours and melanomas. Intraoperative cytology of mammary lesions succeeded in identification of nonmalignant processes and of 94 from 97 carcinomas (remaining 3 having been left for histology). As a rule, intraoperative cytology yielded a prompt information about investigated process' nature which was necessary for defining the extent of surgery, further information was completed by histology.