The objective of this work w a s t o c o m p a r e physiologic parameters of a group of trained horses submitted to 30 and 60km endurance exercises with an average speed of 10 and 15km/h, respectively. One of t h e g ro u p s w a s t re a t e d , o r a l l y, w i t h a n h i p e r t o n i c electrolyte paste before, during and after the task. The results revealed that the administration of the electrolyte paste did not show any deleterious effect on the animals, a n d a l s o s u g g e s t t h a t t h e s u p p l e m e n t a t i o n w i t h a n electrolyte source should contribute for the performance of horses submitted to prolonged efforts.