A highly purified DNA in fibrous state was prepared from the cells of amylase-producing bacteria, Bacillus subtilis var. amylaliquefaciens Fukumoto K-49. The bacteria grown to the logarithmic phase of their growth cycle were harvested by centrifugation and washed with cold 0.14 M saline solution. The procedure for the isolation of DNA was designed for 100 g of wet packed cells. The cells were suspended in 500 ml of 0.14 M NaCl containing 0.14 M sodium citrate. The bacteria were not lysed by a treatment of deoxycholate or SDS but sensitive to lysozyme. Therefore, the cells were lysed by 100 mg of egg-white lysozyme under agitation for 10 minutes at 37℃. After incubation, this viscous lysate was poured into 2 volumes of ice-cold ethanol and centrifuged. The sediment was homogenized in 400 ml. of 6% PAS, then, the suspension was mixed with an equal volume of 90% phenol and stirred for 90 minutes at room temperature. The emulsion was centrifuged at 10,000 r.p.m. for 20 minutes. The resulting upper aqueous phase was removed by suction and poured into 2 volumes of cold ethanol. A white fibrous mass was wound up on the end of stirring rod. The precipitate was dissolved in 50 ml of 2 M NaCl, and deprotenized with chloroform-octylalcohol (8:1) until very little protein was seen at the interface. After the series of deproteinization, the fraction of DNA was precipitated with ethanol and dispersed in 20 ml of 10% CaCl_2 and centrifuged at 10,000 r.p.m. for 30 minutes. The supernatant fluid was poured into 0.3 volume of ethanol and the precipitate was discarded. The fibrous material was removed with a glass rod and dissolved in 2 M NaCl. Finally, Na-DNA was spooled on a glass rod as a white threadlike precipitate from the solution with 2 volumes of 95% ethanol and dried in vacuo after dehydration of ethanol. Thus, fibrous DNA of 90% purity was obtained. The yield of purified product was satisfactory.