Global positioning systems (GPS) are useful tools for measuring distance, speed, and position in grazing horses. Small, inexpensive (<$100) GPS units represent an alternative to expensive animal tracking systems when subject animals are readily accessible. This study evaluates the usefulness of small, inexpensive GPS units in collecting measures of speed, distance, and position for pastured horses, and to characterize these measurements in a group of Thoroughbred mares. Ten Thoroughbred mares, 6–16 years old, were acclimated to a 12 acre pasture 7 d prior to the study date (October 2005). The pasture contained 2 watering troughs and 1 run-in shed, to which there was no interior access. GPS units (Foretrex 101, Garmin International Inc. Olathe, KS) were affixed to halters and activated at 0930 on day 1. Speed and position data recording continued at 30-second intervals for 36 hr. Nickel Cadmium rechargeable batteries (700mAh) were used, necessitating battery changes at 6 hour intervals. Data was downloaded, edited, and analyzed using GPS Utility (Ver. 4.20.9, UK). Position data were evaluated using aerial images of the pasture obtained from Mapquest. Data are reported as means and standard deviations. The average number of data points collected per horse was 4389±30. During the first 24 hr, the average distance traveled was 4.4±0.50 miles. Over the entire 36 hour period, the average distance traveled was 7.1±0.46 miles. The average speed over the entire period was 0.21±0.067 miles/hr. Analysis of differences between night and day, determined by solar radiation, revealed a slight increase in both speed and distance traveled during the night (P < 0.001). Data from this study confirms the usefulness of small, inexpensive GPS units in grazing research. Quantitative speed, distance, and position measurements are exciting additions to our equine nutrition research, allowing increased detail in pasture-based investigations.