Two real-time PCR assays were developed which enable quantification and differentiation between pathogenic Australian isolates of MDV serotype 1 and the serotype 1 vaccine strain Rispens/CVI988. The assays are based on a DNA sequence variation in the 'meq' gene between pathogenic and vaccinal MDV1 which has been confirmed by sequencing of 20 Australian field strains of MDV. Complete specificity has been demonstrated in samples containing pathogenic MDV (n=20), Rispens (3 commercial vaccine strains), or both. The limit of detection of both the Rispens-specific and the pathogenic MDV1-specific assays was 10 viral copies/reaction.