Abstract   

Five hundred and twenty three blood samples (including 301 sheep and 132 goats) were examined in Al-Qassim Region, Saudi Arabia from 1994 to 1997. Theileria hirci was the only blood parasite infecting sheep and goats in this area. The overall infection rate was 20.46 (80/391) per cent in sheep and 7.57 (10/132) per cent in goats. The highest prevalence was recorded during the autumn season, nearly equal in winter and summer seasons, while it was minimum in the spring season. The Sudanese sheep exhibited the highest infection rate with T. hirci, while there was no significant difference in the infection rate between the Najdi and the Naeimi sheep.