Exercise-induced pulmonary hemorrhage (EIPH) occurs in horses that race at high speeds, such as Thoroughbred and Standardbred racehorses. The disease is almost unknown in endurance horses or draft breeds. As a general rule, the more intense the exercise or higher the speed attained, the greater the proportion of horses with EIPH. The prevalence of EIPH varies with the method used to detect it and the frequency with which horses are examined. Almost all Thoroughbred racehorses in active training have hemosiderophages in bronchoalveolar lavage fluid, indicating that all have some degree of EIPH (McKane et al., 1993). The prevalence of EIPH decreases when diagnosis is based on endoscopic examination of horses after exercise or racing. EIPH is very common in Thoroughbred racehorses with estimates of prevalence, based on a single endoscopic examination of the trachea and bronchi, of 43 to 75% (Pascoe et al., 1981a; Raphel and Soma, 1982; Mason et al., 1983). The prevalence increases with the frequency of examination, with over 80% of horses having evidence of EIPH on at least one occasion after three consecutive races (Sweeney et al., 1990). When examined after each of three races, 87% of Standardbred racehorses have evidence of EIPH on at least one occasion (Lapointe et al., 1994), suggesting that EIPH is as common in Standardbred racehorses as it is in Thoroughbred racehorses.