Retinal pigment epithelial dystrophy (RPED) is a progressive retinal degeneration which occurs in a number of breeds of dog. It is characterised primarily by the accumulation of abnormal lipofuscin-like pigment granules within retinal pigment epithelial (RPE) cells of the tapetal fundus. Similar lipopigments accumulate in the RPE in man in a range of diseases and during normal ageing. It is believed that they may result from the incomplete degradation of phagocytosed photoreceptor outer segment membranes and that autoxidative processes and abnormalities in lipid metabolism may be important in their formation. The purpose of this study was to examine these hypotheses, primarily through a study of the Briard dog, a breed in which RPED is particularly prevalent. The RPE lipopigment from affected dogs was analysed and compared with similar pigments from RPE diseases in other species. Lipid and lipoprotein metabolism and plasma antioxidants were studied in normal Briard dogs and in RPED affected dogs of several breeds. The influence of a number of factors on canine RPE in vitro were investigated. Breed and species variation in RPE lipopigments were demonstrated and the pigments that accumulate in RPED were partially characterised. A primary hypercholesterolaemia was demonstrated in Briard dogs and this was further characterised by plasma lipoprotein electrophoresis and precipitation, and apolipoprotein analysis. The results of these lipoprotein and apolipoprotein studies were consistent with the findings of studies of hyperlipidaemia in human retinitis pigmentosa. Abnormalities were also demonstrated in the plasma antioxidants of RPED affected dogs. The studies of canine RPE in vitro demonstrated the effects of a number of factors on the behaviour of these cells in culture. The use of such culture techniques may represent a useful method for further investigation of the initial hypotheses in the light of the findings of this project