Although customarily used for individual identification of guinea pigs, metal ear tags are suboptimal because frequent detachment often results in wounds with inflammation and secondary bacterial infections. Using 60 6-week-old individually housed male Dunkin-Hartley guinea pigs (Cavia porcellus), we conducted an 8-week study to determine the stability of a new nylon tag attached to the center of the pinna. The subsequent tissue reaction was compared with those due to metal tags attached either at the center or near the edge of the pinna. Physical changes in the tagged ear and tag loss were noted during the study period, at the end of which 10 animals per group were selected randomly for euthanasia and necropsy. The tagged ears were collected for histopathologic examination. Loss of the nylon ear tags (10%) over the 8-week study period was significantly less compared with that of metal tags at the center (45%, P < 0.05) or near the edge (100%, P < 0.01) of the pinna. Histopathologically, complete regeneration of epidermis was observed in pinnae tagged with nylon, whereas pinnae with metal tags showed occasional formation of new cartilaginous nodules with no evidence of epithelial regeneration or healing. The nylon ear tag is considered highly reliable and is recommended as a better alternative to the traditional metal ear tag for the identification of individually housed guinea pigs.