Expression of single-chain variable fragment antibody on the surface of filamentous bacteriophage is widely used to make antibodies with pre-defined specificities. Using direct selection on solid phase-bound amyloid-beta 40 peptide, which is a main pathogenic feature of Alzheimer's disease, we obtained single-chain Fv antibody with specific binding activity. The binding epitope of the antibody is located between amino acids 1 and 16 of the peptide antigen. DNA sequencing showed that the gene coding for the single chain Fv antibody consists of 768 bp, and the complementarity-determining regions were deduced.