Ninety transponders (microchips), 45 made of bioglass, 30 made of acid-etched bioglass, and 15 made of bioglass and provided with a polypropylene cap, were inserted into 15 dogs in six different locations: on the left and right side of the head, and on the left and right shoulders, both cranial and caudal to the dorsum. The transponders were left in place for 16 weeks, during which their position was determined by means of an electronic reader and radiographs, and they were then retrieved and examined histologically. A clinical evaluation revealed that about half of the transponders inserted in all the shoulder locations had migrated to some extent, whereas the transponders in the head location had hardly moved. There were no differences in the extent of migration between the different types of transponders. Histological analysis showed that almost all the transponders were surrounded by a thin fibrous capsule with no sign of any gross inflammatory reaction.