Monoclonal antibodies (mAbs) were prepared against the 8597/CV94 strain of turkey rhinotracheitis virus (TRTV). These mAbs were used to investigate antigenic relationships among three strains (8597/CV94, 1162/92 and CVL14/1 strain) of TRTV, together with polyclonal chicken and rabbit antisera to 8597/CV94 strain, and guinea pig antisera to each of the three strains. Thirty mAbs to the glycoprotein (G:3 clones), fusion (F1:6 clones), phosphorylated (P:6 clones), nucleocapsid (N:12 clones), and matrix (M:3 clones) proteins of viral antigen were obtained by cell fusion. Among these, two mAbs to F1 protein showed virus neutralizing activity. The results of ELISA test indicated that some mAbs only reacted to the 8597/CV94 strain, some reacted to 8597/CV94 and 1162/92 strains, and others reacted to all three viral strains. In neutralization tests with the three virus strains, polyclonal chicken and rabbit antisera against the 8597/ CV94 strain showed the same antibody titers. Results with four neutralizing mAbs including two previously reported mAbs [Ref. 21] indicated the titers of two mAbs (Pn2-2E and Pn3-2F) to 8597/CV94 were much higher than those to the other two viral strains. No differences were observed in the titers of the other two mAbs (Pn01-8E and Pn06-4D) against any viral strains. In cross-neutralization tests with polyclonal guinea pig antisera, there was some variations among viral strains. This work demonstrated that the Japanese isolate 8597/CV94 of TRTV is somewhat different in antigenicity from two British isolates from chickens and turkeys.