Abstract. Subgroup-specific peptide-based enzyme immunoassays from each respective G-glycoprotein of the ovine and the bovine respiratory syncytial virus (RSV) were developed to detect RSV-specific IgG responses in cattle. Antigenic peptides from the respective G-glycoprotein were identified from the extracellular central hydrophobic region (amino acids 158-189) located between 2 mucin-rich regions. These antigenic peptides identified by epitope mapping from each G-glycoprotein were synthesized and used to develop the subgroupspecific enzyme immunoassays. The negative cutoff for each enzyme immunoassay was established as the mean optical density of indirect immunofluorescent antibody-negative bovine sera plus 3 SDs. The sensitivity (82.9%) and specificity (100%) of the bovine enzyme immunoassay and the specificity (95.8%) of the ovine enzyme immunoassay were determined by comparison with indirect immunofluorescence (used as the ''gold standard''). The negative and positive predictive values were calculated for each assay. The presence of serum antibody to ovine RSV in cattle implies that this virus infects cattle and may contribute to the pathogenesis of bovine respiratory disease.Economic losses due to respiratory disease in the US cattle industry approximate $1 billion annually. 10 Respiratory syncytial virus (RSV) has been isolated from people (human RSV [HRSV]) and from several animal species, including cattle (bovine RSV [BRSV]), sheep (ovine RSV [ORSV]), and goats (caprine RSV). These viruses are members of the genus Pneumovirus in the family Paramyxoviridae. They are enveloped, single-stranded, nonsegmented, negativesense RNA viruses. 11 The genome encodes 10 viral proteins: 1B, 1C, N, P, M, SH, M2, L, the major glycoprotein (G), and the fusion (F) protein. 3,8 The G and F proteins are present in the membrane of infected cells and in the virus envelope. 16 The attachment protein G has been the most variable antigen among viral strains. 2 The proposed 3-dimensional model for the Gglycoprotein of BRSV contains a hydrophobic globular region (residues 158-189) bordered by 2 hydrophilic densely carbohydrate-coated mucin-like regions. 15 The G-glycoprotein gene from an ORSV strain has been cloned and sequenced and had greater homology to the BRSV gene (and its encoded protein) than to the HRSV gene (and its encoded protein). 2,4 However, the degree of base sequence differences between BRSV and ORSV suggests that 2 subgroups of an ungulate RSV exist. 2,15 Recent RNase protection assays, Received for publication October 26, 1999. reverse transcription polymerase chain reaction amplification studies, and a phosphoprotein profile analysis support the existence of 2 ruminant RSV subgroups. 1,9,17,18 Current knowledge concerning interspecies transmission of RSV strains is limited. Antibodies to BRSV were found in cattle, goats, and horses but were not detected in sheep. 14,20 Recently, serologic evidence of RSV infection in swine has been reported. 5 Respiratory syncytial virus is recognized as an important pathog...