We describe an extraction method that yields up to 25-mu-g of DNA from 1 gram of soil. Samples are processed within 48 h. The purified DNA is 20-25 kb in size and can be digested by restriction enzymes. The soil is vortex-mixed with 6 mL mixing buffer in an Oakridge tube. Polyvinyl polypyrrolidone is added to absorb the humic compounds that interfere with restriction enzyme activity. The entire soil homogenate is treated with lysozyme and Novozym, followed by sodium dodecyl sulfate to lyse the cells. The crude DNA extract is separated from the soil debris by low-speed centrifugation. Finally, the DNA is purified by CsCl gradient centrifugation and extracted with Geneclean.