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Perennial ryegrass staggers (staggers) is a neurotoxic condition that is caused by consumption of grass (Lolium perenne) that is infected with certain Epichlo� fungal endophyte strains that produce toxins that can adversely affect and potentially kill sheep.� Symptoms include head shaking, changes in gait, stiffness and falling. Affected sheep can recover after removing them from pastures containing those endophyte strains.� A study was conducted in Lincoln, New Zealand to determine if the onset of staggers could be identified with GPS tracking and accelerometers.� Fourteen sheep per treatment grazed in either an endophyte-infected ryegrass pasture or an endophyte-free control pasture for 17 days in late March and early April.� Sheep were fitted with collars containing a 3-axis accelerometer recording movements at 12 hertz. Three sheep per treatment were also tracked at 3-minute intervals with GPS receivers. �Sheep were scored by an experienced observer for symptoms of staggers weekly and at the end of the study using a 0 to 5 scale. Control sheep did not display any symptoms of staggers and 10 sheep in the infected pasture displayed little or no symptoms (0 or 1 score).� The other 4 sheep in infected pasture had scores from 2 to 4 at the end of the study.� Sheep grazing in the infected pasture (4350 � 63 m/day) moved slower (P=0.04) than sheep in the control pasture (4727 � 56 m/day). Distance traveled varied among days, but there did not appear to be any temporal trends. Accelerometer data showed clear changes in behavior of affected sheep from the beginning to the end of the study.� Accelerometers may be useful for remotely detecting the onset of perennial ryegrass staggers.