Blood and serum samples were taken from 481 horses, from a stud farm or a racecourse, and tested by microscopic examination of blood smears and cELISA for Theileria equi (T. equi) and Babesia caballi (B. caballi) infections. At the time of sampling, animals were also examined for tick infestations and clinical disease, which were not observed in any of the sampled horses. During the microscopic examination of thin blood smears, parasites were detected in the three horses from the racecourse. Overall seroprevalence of infection was detected as 18.50% (89 of 481 horses) by cELISA, with T. equi being significantly more prevalent than B. caballi. Of the 481 blood samples, 78 (16.21%) were serologically positive for T. equi and 4 (0.83%) were serologically positive for B. caballi. In addition, 7 (1.46%) samples were positive for both T. equi and B. caballi antibodies. Seropositivity rates in the racecourse horses were higher than those determined in the stud farm horses. The rates for T. equi, B. caballi and both species were 13.39, 0.52 and 0% in the horses from the stud farm and 27, 2 and 7% in the racecourse horses, respectively. These results indicate that equine piroplasmosis is more common in racehorses than studhorses and therefore it might be a serious concern in horses that participate to international races. © 2008 Elsevier B.V. All rights reserved.