Twenty-eight paired blood and semen samples obtained from human immunodeficiency virus type 1 (HIV-1) seropositive men at various stages of disease progression were evaluated for titer and immunoglobulin (Ig) class by an enzyme-linked immunosorbent assay (ELISA). Blood antibody titers ranged from 40,000 to 4,000,000 with a median of 40,000. Semen titers ranged from 400 to 40,000 with a median of 400. HIV-1 antibody titers in matched semen and blood samples showed a strong positive correlation (r = 0.963). The ratio of semen:blood titers ranged from 1:1000 to 1:10 with a median of 1:100. There was no correlation between blood or semen antibody titer and stage of disease of the patients. However, there was a trend toward higher (greater than or equal to 4000) semen antibody titers in men with evidence of genital tract inflammation greater than 10(6) white blood cells/ml semen; 3/5 versus 5/23, p greater than 0.1 Fisher exact test). All HIV-1 antibodies detected were of the IgG class; no IgA or IgM class antibodies of titers greater than or equal to 40 were found in either blood or semen. Thirteen paired blood and semen samples from individual patients were analyzed for antibody specificity by Western blot. In some cases antibody profiles in semen were different from those in blood; strong antibody reactivity against the gp160 viral coat antigen band was consistently detected in semen and blood, whereas the prevalence of detectable antibody reactivity against the p55 and p17 HIV-1 antigen bands was significantly reduced in semen.(ABSTRACT TRUNCATED AT 250 WORDS)