Ball et al., 1991: "Evaluation of a microchip implant system used for animal identification in rats." Laboratory Animal Science. 1991;41(2):185—186.

Summary: 40 rats were implanted with subcutaneous microchips. The tissue surrounding the implants was evaluated for adverse reactions after periods ranging from two weeks to one year. (See table below.) No palpable masses or cancerous changes were observed.

Author(s)

Species

# Animals

Length of Microchip Exposure

Developed Cancer

Ball et al., 1991

rats

10

2 weeks

none observed

10

3 months

10

6 months

10

1 year

Note: When Elcock et al. (2001) later studied a larger sample of rats (n = 1,040) over a two-year period, they found a nearly 1% incidence of malignant tumors.