Following computer-assisted analysis of the amino acid sequence of various HIV-1 isolates, we synthesized a series of oligopeptides derived from variable and conserved regions of the envelope protein complex gp120/gp41. The peptides were used in ELISA tests for their reactivity with human antisera from HIV-1 positive individuals; patients with clinically manifested AIDS showed only a rather limited reaction, predominantly with two peptides (p102-112, p316-326), which is in contrast to sera from HIV-1 positive asymptomatic individuals, whose sera were reactive with almost all peptides. Using consecutive sera of the same patients, decreasing antibody titers to defined epitopes could be shown to occur during the development of AIDS. Cellular immune response recognition was analyzed in T-cell proliferation assays by [3H]thymidine incorporation. One peptide localized in a conserved region clearly induced proliferation of T-cells. Those data were combined to a map of the functions localized in the various regions of the HIV-1 envelope proteins.