The main objectives of the design of GB virus C (GBV-C) peptide microarrays are the miniaturisation of antigen-antibody interaction assays, the simultaneous analysis of several peptide sequences and the reduction in the volume of serum required from patients since this always represents a limiting factor in studies to develop new systems for diagnosing human diseases. We herein report the design of a microarray immunoassay based on synthetic peptides derived from the GBV-C E2 protein to evaluate their diagnostic value in detecting anti-E2 antibodies in HIV-1 patients. To this end, peptide microarrays were initially prepared to identify the most relevant epitopes in the GBV-C E2 protein. Thus, 124 peptides composed of 18 amino acids covering the whole E2-protein sequence, with 15 residue overlaps, were spotted in triplicate onto γ-aminopropyl silane-functionalised adsorbent binding slides. The procedure to select the E2 protein epitopes was carried out using serum samples from HIV-1-infected patients. The samples had previously been tested for the presence or absence of GBV-C anti-E2 antibodies by means of the Abbott test. Thus, 11 specific epitopes in the GBV-C E2 protein were identified. Subsequently, peptide antigen microarrays were constructed using the E2 epitopes identified to detect GBV-C anti-E2 antibodies in the serum of HIV-1-infected patients with no known GBV-C co-infection. The 11 peptides selected identified anti-E2 GBV-C antibodies among HIV-1-infected patients, and a reactivity of 47 % was established. The potential antigenic peptides selected could be considered a useful tool for designing a new diagnostic system based on peptide microarrays to determine anti-GBV-C E2 antibodies in the serum of HIV-1-infected patients.