A MONG ANIMALS in general there is a wide variety of parasitic infections in which larval stages migrate through and sometimes later reside in the tissues of the host without developing into fully inature adults. When such parasites are found in human hosts, the infection may be referred to as larva migrans although definition of this term is becoming increasingly difficult. The organisms implicated in infections of this type include certain species of arthropods, flatworms, and nematodes, but more especially the nematodes. As generally used, the term larva migrans refers particularly to the migration of dog and cat hookworm larvae in the human skin (cutaneous larva migrans or creeping eruption) and the migration of dog and cat ascarids in the viscera (visceral larva migrans). In a still more restricted sense, the terms cutaneous larva migrans and visceral larva migrans are sometimes used to denote the formation of lesions due to a particular species of larva known or presumed to be the one most commonly involved: Ancylostorna braziliense in the skin, and To/xocara canis in the viscera. This usage of the terms is incorrect, however, since, as previously emphasized, the character and location of the lesions and the resultant symptoms are unreliable clues in the specific identification of the causative organisms (1).