A severe, naturally occurring enteric disease of cattle in which adenovirus inclusions are present in the intestinal vascular endothelium has been recognized in several countries; three different adenovirus serotypes have been isolated from affected animals. An in situ hybridization technique for the detection of bovine adenoviral DNA was developed and applied to tissue from 13 cattle in Northern Ireland diagnosed to have the disease. Bovine adenovirus serotype 10 (BAV-10) was identified in the vascular inclusions of all cattle, providing strong evidence that adenoviral enteric vascular disease in cattle is associated with this serotype. The existence of BAV-10 has only recently been recognized. The first molecular biology-based technique for the diagnosis of BAV-10 infection is described. The animals in the present study are the first in which BAV-10 has had a confirmed role in a pathologic process.