Simple protocol is used to extract DNA from small numbers of cultured cells and from fragments of soft or bony tissues. The method is used chiefly to genotype transgenic and knockout mice. Each 6-10-mm snippet of mouse tail yields 50-100 µg of DNA that can be used in dot or slot blotting to detect a transgene of interest, in Southern hybridization to detect DNA fragments that are <20 kb in size, and as a template in PCRs.