A poxvirus was isolated during the latter half of 1993 from a black-tailed deer (Odocoileus hemionus columbianus) that died of fulminant adenovirus infection in California (USA). The poxvirus was isolated from a pooled tissue homogenate, after repeated serial blind passages in primary black-tailed deer testicular cells. Based on electron microscopic examination of the virus, we observed morphologic features typical of the genus Orthopoxvirus, although definitive characterization was not done.