This study was carried out to estimate the annual economic impact of tropical theileriosis in areas around Kayseri, Turkey. For this purpose the sera of a total of 717 cattle were examined microscopically and tested using IFAT for Theileria annulata infections between May 1997 and November 1998. At the same time the animals were also examined for tick infestation and the ticks were collected. During the field studies, cattle, which were acutely infected with T. annulata were also investigated.