A group of eight Wagler's pit vipers (Tropidolaemus wagleri) from a private collection died with respiratory signs within 6 mo of one another. The group consisted of an adult breeding pair that was wild caught and six offspring from this pair. Four of the dead snakes were submitted for gross and histopathology. Signs of bacterial pneumonia were detected in all four examined snakes. No inclusion bodies suggestive of viral infection were found in any of the examined tissues. Polymerase chain reactions for the detection of ferla-, adeno-, reo-, and nidoviruses were all negative, but reptarenaviruses closely related to viruses previously described in boa constrictors (Boa constrictor) with inclusion body disease were detected in two of the four snakes. This is the first description of reptarenaviruses in viperid snakes. The pathogenic role of the virus in illness is unknown.