Murasugi et al., 2003: "Histological reactions to microchip implants in dogs." The Veterinary Record. 2003(Sept 13);328.

Summary: Microchips were implanted into nine dogs and later removed after periods ranging from three days to six years (see table below). The chips and surrounding tissue were examined microscopically. Inflammation and encapsulation had occurred, but no tumors or cancerous changes were found.

# of Dogs Evaluated	Length of Microchip Exposure
2	3 days
2	3 months
2	1 year
2	3 years
1	6 years

Excerpt: "As the mean lifespan of dogs as companion animals increases, long-term evaluation of the safety and biological stability of implants is necessary."