The amino-terminal sequence of the B-type coat protein from cucumber mosaic virus was determined by a simple manual Edman degradation with 5 nmol of amino-terminal peptide. This was achieved by a fast, quantitative method of obtaining the anilinothiazolinone or phenylthiohydantoin amion acid, and quantitations were made by either a rapid 15 min-back hydrolysis and amino acid analysis or by a high-performance liquid chromatographic procedure. The amino-terminal residue of the coat protein was acetylated and was identified by a combination of enzymatic cleavage and reversephase high-performance liquid chromatography. On the basis of the analytical data, the amino-terminal sequence of 14 residues was established to be acetyl-Met-Asp-Asp-His-Glu-Leu-Thr-Leu-Ser-Tyr-Ala-Ala-Ser-Lys-.