The cause of the frequent high losses and morbidity in young herons, especially under a year old, has been generally obscure (7). Bowdish (1) and Locke (5) indicated, however, that the nematode Eustrongylides ignotus was the cause of fatalities in herons and egrets on the East Coast of the United States. An excellent description of this nematode has been given by Jagerskiold (4), where he described its presence in bitterns in Europe. Eustrongylidiasis in the great blue heron (Ardea herodias) in the United States was apparently first recorded as a disease by Chapin, in 1926 (2). The present report demonstrates a further geographic distribution, or extension, of this pathogenic nematode and its importance in disease of great blue herons. During May, 1976, about 25 great bliue herons, either dead or unable to fly, were found in open fields of Madison County, Indiana. All appeared to be birds fledged in the previous year. A high number of young herons is generally noted in this area during the weeks of spring migration. Two of the herons which died were necropsied and both showed similar lesions caused by E. ignotus. They were emaciated from the chronic debilitating effects of the existing parasitic infection. Gross lesions of a severe inflammatory nature were seen in the proventriculus and gizzard, and the worms were entwined among each other within the necrotic wall or musculature of each organ (Figs. 1, 2). Interestingly, no peritonitis was present in these birds, which was in contrast to observations made in other cases involving this nematode. Several incomplete specimens which were dissected from the fixed tissues and cleared in glycerin possessed the following char-