Differentiation of herpesvirus isolates has been performed mostly on the basis of biological properties and serology. In this study, 15 herpesvirus isolates from different species of birds were compared by restriction endonuclease analysis of genomic DNA. All herpesviruses were isolated in Europe or are used as vaccine viruses there. The isolates could be differentiated into seven groups based on restriction patterns. The largest group contains isolates from passeriform and psittacine birds and could further be subdivided into four subgroups. Two other groups are represented by herpesvirus isolates of quail and crane, and by isolates of pigeon and owl. Duck plague virus, herpesvirus of turkey, infectious laryngotracheitis virus and a herpesvirus isolate from tragopan all exhibited distinct restriction patterns. In general, our results parallel earlier cross-neutralization studies and yield additional, more detailed information on the relationship between different herpesvirus isolates of birds.