This study tested for the first time an optoelectronic device (Perometer*) measuring limb volume of horses. An analysis of its application was performed regarding the influence of different types of physical exercise on the volume of the extremities. 40 horses were divided into four groups often horses, each group being exposed to exercise, differing in kind and duration of lunging, horse-ridden and riderless. The volume measurement was performed by determining the inactive value (I) after a twelfe-hour standing period, the load value (II) immediately after exercise and recovery value (III) one hour after exercise. The results showed a highly significant decrease in limb volume of 5.7% between values (I) and (II), as well as a highly significant increase of 68% between (II) and (III). The volume changes observed in male horses were significantly higher than in female horses. Volume changes in horse-ridden groups were higher than riderless ones, but not significant. There were fewer leg volume changes at low ambient temperatures (1-12 degrees C) compared to high temperatures (23-31 degrees C), but these were not statistically significant. Well-trained horses showed lower volume changes than less trained horses (not statistically significant). The Perometer is a fast and reliable tool for measuring limb volume of horses. The ICC (Interclass Correlation Coefficient) calculated a high measurement reproducibility of 0.996. A variance analysis showed no significant differences between the three repeated leg measurements. Thus, the Perometer can be used for monitoring and quantifying edema and documenting limb volume changes resulting from training, wearing compression stockings or bandages, manual lymph drainage.