A Theileria sp. piroplasm has been found in cattle from 10 Northland herds. Transmission studies, involving two splenectomized calves, led to its identification as T. orientalis, which has not been previously found in New Zealand. This piroplasm is relatively benign hut can cause severe anaemia in heavily parasitized animals. The cattle tick Haemaphysalis longicornis is considered to be the likely vector.