Amyloid formation occurs via numerous complex mechanisms， often involving intermediates. This study examines the mechanism of amyloidogenesis in two N-terminal fragments of serum amyloid A (SAA)， which are known to exhibit dramatically different amyloid structures. Fibrillization kinetics by these peptides are found to exhibit two unusual features: slower rates at higher peptide concentration， and complete insensitivity to addition of pre-formed seed. Additionally， we find that these peptides form micelle-like oligomers in solution. Our results imply an unusual dual role of micellar oligomers in amyloidogenesis， in which these particles act both as an off-pathway reservoir of peptide， and an inhibitory aggregate that slows amyloid growth. We anticipate that this mechanism of fibril formation may exist in other hydrophobic amyloid-forming peptides and proteins.