PkNBPXa binds to Duffy negative and Duffy positive human erythrocytes. Native PkNBPXa (A) and PkNBPXb (B) present in parasite supernatants were tested for their ability to bind Duffy positive and Duffy negative human cells by EBA. Culture supernatants (S) containing soluble merozoite proteins were incubated with human Duffy positive (Fya+b+) and Duffy negative (Fya-b-) erythrocytes, and then the bound proteins were eluted, electrophoresed and transferred to nitrocellulose membranes. PkNBPXa and PkNBPXb specific antibodies were used to probe the membranes. PkNBPXa was detected in the supernatants and eluates from Duffy positive and Duffy negative erythrocytes. PkNBPXb was present in the supernatant but did not bind to either type of human erythrocytes. As a control, erythrocytes were incubated in the absence of supernatants and no PkNBPXa specific bands were detected in those samples (R).