Bovine peripheral blood mononuclear cells (PBMCs) and monocytes were stimulated with bovine herpesvirus 1 (BHV-1), LPS and concanavalin A (Con A) to produce L-arginine-dependent nitric oxide (NO) in vitro. NO was detected as early as 12 hrs and up to 72 hrs post stimulation (p.s.). The NO from lipopolysacharide (LPS)-stimulated PBMCs and monocytes was found to exhibit antiviral effect against BHV-1. The anti-BHV-1 effect was inhibited with N(omega)-methyl L-arginine indicating involvement of inducible NO synthase (iNOS) in NO production.