Delineation of HIV-1 neutralizing antibody specificities of polyclonal sera is important for better understanding of humoral immune responses and vaccine design. Our web server, NFPws, is an efficient computational method to predict the antibody specificities of a serum using the serum pattern of neutralization against a diverse panel of HIV-1 isolates. In addition to the known antibody specificities, NFPws also predicts the presence of random signal/antibody specificities.