V ASCULARIZATION of the cornea may be produced experimentally in animals by various means. Rabbits, dogs, rats and guinea pigs have been used with uniform success, and there is no evidence that a particular species or strain is more susceptible than another. Maintenance on a stock laboratory diet is generally accepted to be a safeguard against the spontaneous development of the condition. However, corneal invasion was discovered in a group of supposedly normal gray Norway rats that were not known to be suffering from any dietary deficiency or other pathogenic condition. Albino rats in the same colony were found to be free of corneal vascularization. METHOD The rats were born and raised in the Wistar Institute animal colony and ranged in age from 64 to 766 days. Their diet consisted of Purina dog chow pellets ad libitum, and greens (principally lettuce) given twice each week. This diet is theoretically adequate