The present invention provides human monoclonal antibodies, derived from the murine mAb NM-01 (PCT/US92/07111), which are specifically reactive with HIV gp120 and have the capacity to neutralise the infection of H9 cells in culture by live HIV-1 strains MN and IIIB as shown by reverse transcriptase, p24 and syncytium formation assays. These antibodies were shown to be as or more effective than the parent murine antibody by the aforementioned criteria.