Encapsulated as well as unencapsulated fourth stage larvae of Eustrongylides sp. were found in four northern water snakes, Nerodia sipedon, from Virginia. Unencapsulated nematodes occurred within muscle, subcutaneous tissue and in the coelom. Encapsulated nematodes occurred in three forms: recently encapsulated, degenerating, or sclerotic; they were found on the mesentery, in muscle and subcutaneous tissue. Encapsulation was associated with muscular hypotrophy, fibroplasia and eosinophilia.