The beta-amyloid proteins (A beta), especially the variant A beta 1-42, are the primary constituent of the amyloid plaques which are characteristic of Alzheimer's disease (AD). The C-terminus of A beta has been identified as crucial for rapid amyloid formation. A 9-residue C-terminal fragment of A beta (designated beta 34-42, with sequence LMVGGVVIA) forms a structured aggregate which is classified as an amyloid fibril based primarily on its morphological and solubility properties and the classic cross-beta fiber diffraction pattern it displays. We have adopted this aggregate as a model of the A beta-dominated amyloid plaques associated with AD. Previous results from a series of internuclear C-13-C-13 distance measurements along the peptide backbone indicate that the beta 34-42 backbone conformation differs considerably from that of the classic beta-sheet, possibly including an unusual cis amide bond in the peptide's central glycyl-glycyl region. Here we report evidence which demonstrates the presence of a trans configuration at the peptide linkage between these residues. The evidence derives from solid-state NMR static echo and n = 2 rotational resonance experiments which probe the orientation of the C-13 carbonyl chemical shift anisotropy (CSA) tensor of the peptide bond with respect to the dipolar tensor connecting the carbonyl carbon to the C-13-labeled alpha-carbon on the succeeding residue.