The monkeypox virus (MPXV) outbreak in 2022 has renewed interest in the detection of antibodies against orthopox viruses (OPXV) and MPXV, as serological methods can aid diagnostics and are key to epidemiological studies. Here three complementary serological methods are described with different strengths to aid the development and evaluation of in-house assays: An immunofluorescence assay (IFA) for specific detection of IgG and IgM, an enzyme-linked immunosorbent assay (ELISA) for higher sample throughput to aid epidemiological studies and a neutralization test (NT) to detect virus neutralising antibodies. As implementation of MPXV-specific diagnostics is often hampered by the requirement for a dedicated biosafety level 3 laboratory (BSL-3), the focus is on biosafety aspects to facilitate safe testing also under BSL-2 conditions. To this aim, IFA and NT titres of sera are compared after MPXV or cowpox virus infection or vaccinia virus immunization by using both homologous and heterologous antigens. Because of a large degree of cross-reactivity, vaccinia virus could be used as a less virulent alternative to MPXV, as VACV can be handled under BSL-2 conditions. Furthermore, an inactivation method to remove potentially infectious virus particles from viraemic sera without compromising antibody detection was developed. Although the existing immunological cross-reactivity between OPXV prevents species differentiation by general serological methods, it also provides an opportunity for the interchangeable usage of different OPXV species in serological assays, enabling MPXV serology outside of BSL-3 facilities.