Biogenic siliceous and calcareous sediments were drilled at sites 677 and 678 on the flank of Costa Rica Rift in the Panama basin. We analysed DCAA (dissolved combined amino acids) and DFAA (dissolved free amino acids) in the interstitial waters as well as THAA (total hydrolyzable amino acids) in the sediments in order to evaluate the relationship between THAA, DCAA and DFAA. Comparison of the THAA in the sediments and in marine settling particulate matter (Ittekkot et al., 1984 b) showed that the concentration of non-protein amino acids (e. g., beta-alanine, gamma-aminobutyric acid, and ornithine) was much higher in the sediments and that the neutral amino acid fraction was depleted in the sediments. These results, together with the organic carbon profile, indicated that the production of non-protein amino acids occurred mainly at shallow depth but still continued through the sedimentary column, at a slow rate and that the neutral amino acid fraction was more liable to decomposition than the acidic and basic amino acid fractions. The positive correlation between total DCAA and the DFAA and the weak correlation of the total amino acid concentrations between the interstitial waters and sediments suggested that biological and/or chemical reaction rates between the DCAA and the DFAA were much higher than the digestion and/or transformation rates of the THAA in the sediments. The higher ratio of neutral to acidic amino acid fractions in the DFAA than in the DCAA was attributed mainly to reaction or adsorption with carbonates and partly to the contribution of decomposed products of the neutral fraction in the THAA of the sediments.