Abstract: Novel anti-idiotype monoclonal antibodies are described which are capable of specifically reacting with the idiotype of human anti-gp120 antibodies, of inhibiting the binding between the gp120 antigen and human anti-gp120 antibodies, and of evoking a neutralising anti-gp120 immune response in an animal host to which they are administered. The anti-idiotype antibodies of the invention can be identified based on the amino acid sequences of the variable portions of their light and heavy chains. In addition, a method for obtaining a panel of anti-idiotype monoclonal antibodies, expression vectors and transformed host cells usable in a recombinant DNA procedure in order to generate the aforesaid anti-idiotype monoclonal antibodies, as well as the therapeutic, prophylactic and diagnostic use of such antibodies are disclosed.