A new method has been developed by us to observe the movements of the abomasum by using a magnet and digital magnetometer. Four cows with left displacement of the abomasum underwent conventional correction by rolling without tacking. A doughnut-type magnet was sutured to the pyloric region in a routine operation. The same was done in three control cows. The position of the pyloric region was observed with a digital magnetometer from outside the cow's body. The magnets in the pyloric region of the control cows were located at the right side of the abdominal cavity at 10-30 cm anterior to the udder base, and moved slightly in various directions within the span of a day. On the other hand, the magnets in the pyloric region of cows with abomasal displacement moved widely in the abdominal cavity from the normal right side to the abnormal left front side. A large movement of the magnet from the normal right side to the abnormal left side of the abdominal cavity was observed within 12 h of the onset of abomasal displacement.