Polyalanine sequences of varying length and tethered to a solid support are studied in atomic detail by high-resolution magic angle spinning (HR MAS) NMR. At high densities, it is shown that aggregation of the sequences is at the origin of synthetic difficulties. Decreasing the peptide density by discharging the resin allows study of longer sequences without being hampered by aggregation, and a helix formation has been observed for the (Ala)(12) sequence. This demonstrates that the combined use of solid phase synthesis and high resolution magic angle spinning NMR spectroscopy is a new tool that can be used advantageously in the study of aggregating structures.