The development of an enzyme linked immunosorbent assay for the detection of antibodies to equid herpesvirus type 1 in horse sera. Bachelor of Philosophy 1983 Peter Dudley Jolly Abstract An Enzyme Linked Immunosorbent Assay (ELISA) was developed to detect antibodies against equid herpesvirus type (EHV-1) in equine sera. Several methods of ELISA antigen preparation were examined in an effort to find the one most suitable for seroepidemiological purposes. The antigens were compared by titrating them against 32 foal sera with wide ranging serum neutralization test (SNT) titres to the same strain of EHV-1. ELISA antigen prepared by polyethylene glycol precipitation of a crude EHV-1 infected cell culture extract was found to perform similarly to highly purified EHV-1 virus. Logit transformations of individual serum titration curves were used to titre sera and to compare titration curves generated by each antigen. Significant differences (P<0.01) were found between slopes of titration curves generated by each antigen preparation, however end point titres showed a high degree of correlation e.g., 98.9% for crude vs highly purified virus extracts. The use of highly purified virus as ELISA antigen produced antibody titres that showed the best correlation with the SNT, and that best differentiated neutralising antibody titres. However, differences observed between antigen preparations were small, and for practical reasons such as relative ease of production, economy, and high yield, the crude infected cell culture extract was chosen for subsequent use. Comparisons of ELISA and SNT antibody titres over a larger number of foal sera showed a high correlation (71.9%), with ELISA titres being approximately 100 to 100,000 times greater than those of SNT. Approximately one-half of the sera negative by SNT were positive by ELISA, but the majority of these had low ELISA titres. No sera tested were negative by ELISA and positive by SNT. It was concluded that the ELISA developed in this study was ahighly sensitive and specific method for the detection of antibodies to EHV-1 in equine sera.