To confirm the genetic stability of the Edmonston–Zagreb vaccine strain, we determined and compared the nucleotide sequences of genuine Edmonston–Zagreb master seed (EZ D22) and current working seed lot (EZ D24 2/99). Sequence analysis and comparison of the two sequences confirmed that these two sequences are the same at the molecular level. The obtained sequences were also compared to reference strains, i.e. Edmonston wild-type (Edmonston Wt) AF266288 and Edmonston–Zagreb (EZ) AF266290 vaccine strain. The sequence of EZ D22 differed from the Edmonston Wt in 32 nucleotides. EZ D22 differed from EZ AF266290 in six nucleotides. Coding substitution at position 441 and two silent substitutions at positions 11999 and 14612 in the L gene are unique to EZ D22. The differences found between EZ from different sources can be a good reason for periodical sequence analysis of the same strain in the hands of different manufactures.