The volatile substances stripped from crushed sporophorus of Lentinus edodes were analyzed by chromatographic procedures. Three of 8 major components behaved as carbonyl compounds; 2 of them were identified as acetaldehyde and propionaldehyde, respectively, and the remaining one appearing to be a sulfur-containing unsaturated aldehyde was left unidentified. Five sulfur compounds were also detected in the stripped volatiles; 3 of them were characterized as methylmercaptan, methylsulfide, and dimethyldisulfide, respectively; all of which appear to contribute significantly to the flavor the crushed mushroom bearing. Free formaldehyde contents in fresh and dried mushrooms were measured colorime-trically after the dimedone-chromotropic acid reaction. In any case formaldehyde contents were found never to exceed above 40μg per g of the mushroom on dry weight basis. On contrary, a significant amount of formaldehyde was found to be evolved on refluxing the mushroom extracts in 2% phosphoric acid, i. e. under the conditions that were much the same as those of steam distillation adopted in the official methods of analysis for formaldehyde. Evidences were given for evolution of formaldehyde via an acidic decomposition of lentinic acid during the refluxing procedure.