We have engineered a novel beta-amyloid peptide variant that expresses a single peptide with two beta-amyloid coding regions linked with a flexible "linker" region. A similar single chain dimer has been generated for superoxide dismutase, leading to a functional enzyme. We find that this beta-amyloid single chain dimer, although containing the beta 1-42 sequence, fails to make amyloid dye-reactive deposits. One interpretation of this result is that the linker region constrains the folding of this peptide, thus preventing amyloid formation.