Two model peptides Ala-Ser-Asp-Tyr-Leu and Ala-Ser-Glu-Tyr-Leu have been synthesized and coupled with an without protecting groups to the amino groups of polystyrene resins. The yield in the binding operation was 93-97% by using water-soluble carbodiimides as condensing reagents. Edman degradation of the products and quantitative estimation of the amino acid phenylthio-hydantoins, as well as amino acid analysis of the partially and completely degraded resins, showed about 7-10% of the fixed peptides not to be involved in the degradation procedure. That part of the material which was not involved in the Edman degradation during the first step also remained inactive in the following degradation operations. The analytical data presented in the paper explain not only the course of the Edman degradation of peptides linked via the side-chain carboxylic groups to the resin, but they also describe the chemical reactivity of the various carboxylic groups in the binding operation. 22% of the peptides are bound to the resin by side-chain carboxylic groups in the case of the aspartate-containing peptide, 26-27% in the case of the glutamate-containing peptide. 75-77% and 72-75% respectively of the peptides are fixed to the resin via the C-terminal carboxylic group. No more than 3% of the fixed material may be bound bifunctionally to the support.