i. A clinical study has been made of 401 cases of tumours of salivary tissue and the results reported; familial incidence being noted on 3 occasions. ii. A histological study has been made of those cases seen at the Southern General Hospital, Glasgow. Attempts were made to clarify the presence or absence of "cartilage" in pleomorphic adenomata using Sulphur-35 with no result. iii. Blood-grouping was carried out in 341 patients from this series, and a highly significant preponderance of group-A was noted as compared with the control series. This preponderance was also present in the separate types of salivary tumours as well as in salivary tumours in general. iv. The results of attempts to produce salivary tumours experimentally in animals is discussed. v. The literature is reviewed in all parts of the thesis.