The growth kinetics of neuropathogenic and non-neuropathogenic equine herpesvirus type 1 (EHV-1) strains in fetal horse kidney (FHK) and mouse cerebral cortex cell line were compared. The relevance of the aspartic acid/asparagnic (D/N) amino acid change at position 752 of open reading fram (ORF) 30 was examined in Japanese isolates. Neuropathogenic strains 01c1 exhibited similar growth kinetics to nonneuropathogenic strain 90c16 in FHK and cultured neurons. Open reading fram (ORF30) (DNA polymerase) mRNA expression levels by real-time RT-PCR were the same among the FHK cells infected by both virus -strains. The amino acid encoded at 752 of ORF30 in 01c1 was aspartic acid; while asparagine was encoded in 90c16 strains isolates. The D/N752 difference in ORF30 may not be related to replication ability in FHK and neurons cell line.