Detection of gene amplification in human cancer cells has both clinical and biological importance. Amplified genes can be classified in one of two categoriesas oncogenes or as genes conferring drug resistance. Both types of gene amplification may alter clinical management of the patient. The basic protocol describes preparation and quantitation of DNA from tumor tissue and the use of conventional Southern blot hybridization analysis to detect and quantify gene amplification. The first alternate protocol provides an approach to quickly screen tumor samples for gene amplification using slot blot hybridization analysis. The second alternate protocol describes the use of the polymerase chain reaction (PCR) for analyzing tumors that may be difficult to analyze because of degradation or limited amounts of DNA. A explains the proper methods for obtaining, processing, storing, and shipping tumor tissue for DNA analysis.