Theiler was the first Director of the Onderstepoort Veterinary Research Institute, outside Pretoria. This institute under his leadership carried out research on African horse sickness, sleeping sickness, malaria, East Coast fever (Theileria parva) and tick-borne diseases such as redwater, heartwater and biliary. The University of Pretoria Faculty of Veterinary Science was established there in 1920 which enabled veterinarians to train locally for the first time.