Monoclonal antibodies (mAbs) that neutralize human immunodeficiency virus (HIV) can be used as microbicides to help prevent the spread of HIV in human populations. As an industry standard, HIV-neutralizing mAbs are produced as recombinant proteins in mammalian cells, but the high manufacturing costs and limited capacity reduce the ability of target populations in developing countries to gain access to these potentially life-saving medicines. Plants offer a more cost-effective and deployable production platform because they can be grown inexpensively and on a large scale in the region where the products are required. Here we show that the maize-derived HIV-neutralizing mAb 2F5 is assembled correctly in planta and binds to its antigen with the same affinity as 2F5 produced in mammalian cells. Although 2F5 has been produced at high levels in non-plant platforms, the yield in maize seeds is lower than previously achieved with another HIV-neutralizing mAb, 2G12. This suggests that the intrinsic properties of the antibody (e.g. sensitivity to specific proteases) and the environment provided by the production host (e.g. the relative abundance of different proteases, potential transgene silencing) may combine to limit the accumulation of some antibodies on a case-by-case basis.