The prevalence of orthopox virus (OPV)-specific antibodies in 1,040 red foxes (Vulpes vulpes) was evaluated on a large scale in the German Federal State Brandenburg. Serum samples were selected from 809 communities within the study area from January 1991 to September 1994 by simple random sampling. Screening was carried out by an indirect enzyme-linked immunosorbent assay (ELISA). Orthopox virus-specific antibodies were found in 162 (16%) of the 1,040 fox sera. Furthermore 154 (15%) sera were considered suspect positive. The specificity of the antibodies detected in ELISA-positive and suspect positive sera was confirmed by Western blotting. Presence of OPV-antibodies occured in 291 communities. No correlation of OPV-antibodies findings to latitude or characteristic topographical and ecological peculiarities of the study area was found. Although the causative agent is still unknown we believe that orthopox viruses probably have a ubiquitous presence among red foxes.