Doctor Scientiae (Odontology) - DSc(Odont) / Investigations of pathoses of the oral cavity encompass a relatively wide spectrum of diseases, abnormalities, tumours and tumour-like conditions affecting and occurring in the dental hard tissues and supportive structures, the bony skeleton of the face and the soft tissues of the. mouth. It involves a study of the normal - oral biology - and the abnormal - oral pathology. Oral pathology is a relatively new specialized field of dental science and practice. In South Africa, prior to the nineteen-fifties, research in oral pathology was primarily directed towards dental disease. Two people - Julius Staz of the University of the Witwatersrand and Tony Ockerse of the University of Pretoria - were the doyens in this field and made major contributions to dental science. Staz reported on the status of dental caries and tumorous malformations of teeth and Ockerse on the prevalence and severity of fluorosis in South Africa. During the fifties a second generation of dental surgeons, who were interested in soft tissue, bone and tumour pathology, emerged. They ,were Bertie Cohen, George Baikie, Mervyn Shear and John Lemmer who, at that time, were all from the University of the Witwatersrand. Bertie Cohen later joined the Royal College of Surgeons of England. Mervyn Shear led the field with his research on cysts of the oral cavity. The practice of oral pathology, moulded on anatomical pathology, was established in the early sixties and Mervyn Shear and the author, from the University of Pretoria, became known as oral pathologists. Research at that early stage comprised clinical and histological observations of oral lesions, diseases, tumours and tumour-like conditions. Observation techniques became more sophisticated during the sixties and seventies with the advent of histochemistry and electronmicroscopy. The next major development which blossomed in the seventies and early eighties was the application of epidemiological methods in the study of disease. Epidemiological principles enabled the correct recording of profiles of oral pathoses in the community. Much was learnt about the prevalence and distribution of oral conditions. The application and use of experimental models, especially laboratory animals, became popular in the eighties. Amongst others, a germfree animal unit was established in the Faculty of Dentistry of the University of Stellenbosch enabling workers to study the microbiological aetiology of dental and oral disease. Morphological observations of tumours and mucosal lesions were further enhanced during this period with the development of immunocytochemistry Experimental cell studies by means of cell culture techniques, commenced late in the eighties and was established in the early nineties. These models fostered molecular biology techniques which have become useful tools for the investigation of the aetiology of disease at a cellular and molecular level. At present molecular techniques are also popular in other spheres of oral pathology such as microbiological, immunological and oncological research. The author's first contact with oral pathology as a subject, forming an important and interesting part of dentistry, was the prescribed textbook "Oral and Dental Diseases", 2nd ed., 1951., by HH Stone of the University of Liverpool in the United Kingdom. Subsequently an enduring interest in the subject and research was cultivated by three teachers and colleagues, Ivor Kramer, Robert Bradlow and Mervyn Shear. Ivor Kramer, Professor of Oral Pathology in the Eastman Dental Institute of the University of London was a superb postgraduate teacher of oral pathology, and revelled in research. The Dean of the Institute, Professor Sir Robert Bradlow was a clinician and splendid diagnostician. He correlated the clinical and histopathological features of oral diseases. These two teachers set the course in oral pathology for the author during his postgraduate studies. In the sixties, after a spell at the University of Pretoria, the author joined Professor Mervyn Shear at the University of Witwatersrand. It was here that the author could further his skills of presenting lectures and research papers in an orderely manner and strengthen his love of research. The research carried out by the author reflects to a large extent the development of research in oral pathology in South Africa since 1960.. It includes studies of diseases and lesions of the oral mucosa, the dental hard tissues, tumours of the oral cavity and jaws and forensic odonto-stomatology. To date 139 articles have been published and accepted in scientific journals of which I was the first or co-author. The research presented here, however, comprises only those studies related to pathoses of the oral mucosa as it occurs in South Africa. Fifty-four papers and two abstracts are submitted. The papers are grouped into two divisions which include studies on (I) normal human oral and ectocervical mucosa and (II), those related to pathoses of the oral mucosa. The latter is subdivided into sections on: the profile of lesions of the oral mucosa in the community; cytological, clinical and morphological features of lesions of the oral mucosa; and studies on the aetiology of lesions of the oral mucosa. Each division and section is preceded by a declaration as to the contribution of the author or co-authors and a précis of the aims, objects and research findings. In the introduction of the précis statements are made explaining the aims of the study. These statements are not referenced because they appear in the respective articles.