Groups of calves were infected by the injection of ground-up-tick supernatant from ticks infected with ODE-Anand stock of Theileria annulata, the causative agent of tropical theileriosis. Treatment with long-acting oxytetracycline, at 20 mg kg-1, injected intramuscularly, had no effect against severe Theileria annulata infection when administered either as a single injection on the day of infection or as three injections given on days 8, 10 and 12 after infection. Halofuginone lactate, given orally at 1.2 mg kg-1 was effective but caused anorexia, diarrhoea and debility. Parvaquone at 20 mg kg-1 intramuscularly given on day 11 after infection, had a marked suppressive effect, while buparvaquone was highly effective. A single treatment with buparvaquone, either at 5 mg kg-1 or 2.5 mg kg-1 intramuscularly, rapidly eliminated schizonts and piroplasms of T annulata. At 5 mg kg-1 it resulted in rapid recovery of all the treated calves.