The major amyloid-beta (Abeta) peptides found in the brain of familial and late onset Alzheimer's disease include the full-length Abeta1-42 and N-terminally truncated, pyroglutamylated peptides Abetap3-42 and Abetap11-42. The biophysical properties of Abeta1-42 have been extensively studied, yet little is known about the other modified peptides. We investigated the aggregation kinetics of brain-specific Abeta peptides to better understand their potential roles in plaque formation. Synthetic peptides were analyzed individually and in mixtures representing various ratios found in the brain. Spectrofluorometric analyses using Thioflavin-T showed that the aggregation of Abeta1-42 was faster compared to Abetap3-42; however, Abetap11-42 displayed similar kinetics. Surprisingly, mixtures of full-length Abeta1-42 and Abetap3-42 showed an initial delay in beta-sheet formation from both equimolar and non-equimolar samples. Electron microscopy of peptides individually and in mixtures further supported fluorescence data. These results indicate that Abeta-Abeta peptide interactions involving different forms may play a critical role in senile plaque formation and maintenance of the soluble Abeta pool in the brain.