53 individuals negative for anti-HIV by screening test and 79 individuals positive for anti-HIV were prospectively surveyed for clinical progression and by quantitatively measuring anti-p24 (antibodies against an HIV core protein), anti-gp41 (antibodies against an HIV surface protein) and HIV-(p24) antigen. The patients were classified into four categories of HIV-markers: 1. Anti-p24 in high concentrations, HIV-Ag negative, 2. anti-p24 in high concentrations, HIV-Ag positive (most often transitory only), 3. anti-p24 absent/deficient, HIV-Ag negative and 4. anti-p24 absent/deficient and HIV-AG positive. Within a minimum of 18 months, 4 of the 53 (8%) initially anti-HIV negative individuals contracted HIV infection. 17 of the 79 (22%) initially anti-HIV positive individuals showed disease progression. 8 of the patients in category 4 already had AIDS when entering the study, and 3 of the 6 (5%) remaining patients of this category developed AIDS. Amongst the 19 patients in the third category 2 individuals (11%) developed AIDS and in a further 5 (26%) individuals the disease progressed but in no case to AIDS. None of the patients of the categories 1 and 2 developed AIDS but 2 of the 10 (20%) individuals in the second category and 3 of the 29 (10%) in the first category showed disease progression but not to AIDS. In conclusion, the quantitative measurement of anti-p24 and of HIV-Ag affords prognostic pointers for the clinical outcome of HIV infection.