Volcanic ash samples obtained after the May 18, eruption of Mount St. Helens, Washington, were analyzed for organic compounds. Several n-alkanes, fatty acids, dicarboxylic acids, alcohols, phenols, aldehydes, aromatic acids, aromatic and polycyclic aromatic hydrocarbons and chlorinated aromatic compounds were identified by GC-MS. Pyrolysis of plants and soil organic matter is the most probable source of these compounds.