Sera from hemophiliacs were analyzed for antibodies to human immunodeficiency virus type 1 (HIV-1) by using radioimmunoprecipitation (RIP), western blotting (WB) with nonreducing buffer (NR), and WB with reducing buffer (R). We analyzed envelope gp160, gp120, and gp41; pol gene proteins p64, p53, and p34; and gag gene protein p24. Of 215 samples positive for reactivity to gp160 and gp120(RIP), antibodies to p24 were undetectable in 2 (0.9%), to gp41 in 9 (4.2%), to the pol antigens in 5 (2.3%), to gp120(NR) in 3 (1.4%), and to gp120(R) in 55 (25.6%). By sequential analysis of samples, antibodies to gp120(NR), gp120(R), p24, gp41, p64/53, and p34 were observed later in the course of infection than were antibodies to gp120(RIP) or gp160. This result suggests caution against reliance on WB as the "gold standard." A significantly higher rate of progression to AIDS-related complex was found for individuals lacking antibodies to gp120(R). It is possible that antigenic domains represented by gp120(R) may play a role in the pathogenesis of HIV-1 infection.