The research is based on material collected from 110 duikers ( Sylvicapra grimmia ) in Malawi, Rhodesia and Zambia. The habitats of the duiker in Central Africa are described and also various other aspects of ecology. The feeding and management of the animal is discussed, fostering youngsters on to goats being found more successful than rearing on the bottle. The technique of splenectomy is described. Acepromazine was used for sedation and intravenous thiopentone sodium for anaesthesia, the latter being maintained with ether when necessary. Plasmodium (Vinckeia) brucei and P. (V.) cephalophi were rediscovered in Malawi. P. (V.) brucei is described in detail from blood films and compared with P. (V.) cephalophi . The organism was transmitted to another duiker by blood inoculations. The course of the blood infection in a naturally infected splenectomized antelope is described. Attempts to find the vector and exoerythrocytic stages were unsuccessful. Theileri -like trypanosomes, i.e. Trypanosoma (Megatrypanum) spp.—were frequently found in duikers. The parasites have been recorded from at least 23 different species of ruminants. The organisms from duikers are easily cultured on artificial media but difficult to maintain. Attempts at transmission by blood inoculation produced inconclusive results and the vector of the duiker parasite was not discovered. It is possible that the duiker is the host of more than one species of Trypanosoma (Megatrypanum) . Detailed morphological studies, however, of the trypanosomes using biometrical methods failed to reveal any clear-cut statistical difference between the parasites in different duikers from different localities or between the parasites from duikers, cattle and other ruminants. It is considered preferable at this stage not to include T (M.) ingens, T (M.) tragelaphi and T. (M.) cephalophi in the synonymy of the older species T (M.) theileri , although they may conveniently be referred to as ‘ theileri -like trypanosomes’. A brief description of other trypanosomes found in the duiker is given and other records are mentioned. Just under 2 % of the duikers in this survey were found to be infected with piroplasms, probably Cytauxzoon sylvicaprae . A detailed description of the organisms is given. Several duikers in Rhodesia and Malawi were found infected with Sarcocystis . The duiker appears to be a new host record for this parasite. The spores of the organism, as seen in blood films, presumably released from ruptured cysts, are described. The parasite may be a new species of Sarcocystis .