The standard method to recover fragments of DNA from polyacrylamide gels is the "crush and soak" technique. The eluted DNA is generally free of contaminants that inhibit enzymes or that are toxic to transfected or microinjected cells. The method requires time but little labor and results in recovery of <30%-90%, depending on the size of the DNA fragment. It can be used to isolate both double-stranded and single-stranded DNAs from neutral and denaturing polyacrylamide gels, respectively. The method is widely used to isolate synthetic oligonucleotides from denaturing polyacrylamide gels. DNA recovered from polyacrylamide gels by crushing and soaking is generally suitable for use as a hybridization probe, as a polymerase chain reaction (PCR) primer, and as a substrate in enzyme-catalyzed reactions.