Two proteins, YL41 and YL43, were isolated from 80S ribosomes of Saccharomyces cerevisiae by filtration through a Sephacryl S-200 column and by chromatography on a column of carboxymethylcellulose. Their amino acid compositions are presented. Twenty-four proteins including these two proteins were subjected to sequence analyses by automated Edman degradation. Amino-terminal amino acid sequences were determined for 17 proteins,YS3, YS9, YS23, YS24, YS29, YL6, YL8, YLll, YLI5,YL17, YL23, YL28, YL33, YL37, YL39, YL41, and YL43.YL41, which has a 72.7% lysine and arginine content, was found to be particular to eukaryotic ribosomes. The amino-termini of another seven proteins, YS2, YS5, YS8, YS12,YS13, YS20, and YS27, were suggested to be blocked. Comparison of the amino-terminal sequences with all other ribosomal protein sequences so far available indicates that YS9 shows sequence homology to rat liver ribosomal protein S8 (Wittmann-Liebold et al. 1979).