The invention features immunoreagents which neutralize the Human Immunodeficiency Virus Type 1 (HIV-1) by binding to a novel conserved epitope of the HIV-1 gp120. These immunoreagents exhibit a broad neutralizing effect upon HIV attachment to host cells, and are therefore useful in the detection, prevention, amelioration and treatment of HIV disease, primarily AIDS (Acquired Immunodeficiency Syndrome) and ARC (AIDS Related Complex). More particularly, the invention relates to novel human monoclonal antibodies selectively reactive to a conserved conformation dependent determinant of the HIV-1 gp120, derivatives thereof, cell lines that produce these antibodies, and the use of the monoclonal antibodies and their derivatives for the detection, prevention, amelioration and treatment of HIV related disease.