The usage of glycoprotein E (gE)-deleted BHV-1 marker or DIVA (differentiating infected from vaccinated animals) vaccines in combination with the accompanying determination of gE-specific antibodies is one of the basic parts of BHV-1 eradication programs in Germany. Following the adoption of the "Legislation for the protection of cattle holdings from an infection with Bovine Herpesvirus Type 1" in 1997, several million gE-antibody assays were conducted. Up to now, commercially available gE-blocking enzyme linked immunosorbent assays (ELISAs) are the only test systems available for the detection of gE-specific antibodies. However, there are some difficulties to meet the high requirements on their performance. Therefore, role and function of gE in the virus and the host as well as the principle of gE marker assays, the test design and the capability of the mainly used ELISAs are illuminated in this paper. Additionally, suggestions concerning the optimal usage and the correct application of gE-blocking-ELISAs are discussed.