Immunization of mice and rats with purified external glycoprotein gp120 from two divergent human immunodeficiency virus type 1 (HIV-1) isolates resulted in the development of seven hybridomas secreting monoclonal antibodies able to recognize regions of gp120 which are common among divergent strains of HIV-1. These monoclonal antibodies cross-reacted with env glycoproteins from one African (Rutz), one Haitian (RF), and three North American viral isolates, namely IIIB, MN, and 451 by either immunoblot or radioimmunoprecipitation assays. All recognized denatured gp120 in immunoblots with the exception of one which required a conformationally intact glycoprotein for reactivity. The gp120 epitopes identified by these antibodies were mapped by screening of an env gene library in the lambda gt11 expression system. Three out of four epitopes were found to reside in the amino-terminal half of gp120 (Cys9 to Cys35, Thr44 to Glu72 and Val108 to Met130), the other was located in the middle region (Thr221 to Ser255). By virtue of their extent of cross-reactivity these reagents might provide a unique resource for the detection of new viral isolates related to HIV-1.