Thirteen isolates of egg drop syndrome (EDS) virus were compared by restriction endonuclease analysis of the virus DNA. One virus, an Australian chicken isolate, was distinguished from the others using the endonucleases EcoRl, BamUl, Kpnl, Hindlll, Pstl and Pvull, all of which recognise six base pair DNA sequences. Polyacrylamide gel restriction fragment patterns generated by Haelll, Hhall and TaqI, which recognise four base pairs, allowed further differentiation of the virus isolates. Nine chicken viruses isolated in the United Kingdom and Belgium in the period 1976 to 1987 were identical and could be distinguished from three United Kingdom duck isolates. The Australian isolate, in addition to possessing a DNA deletion (0.4 kbp) at one end of the genome (32.6 kbp) also differed from the European isolates at base sequence level. Genome maps for EcoRl, BamHl, Kpnl and Pstl are reported for the 127 isolate of EDS virus.