Amplified Differential Gene Expression (ADGE) and DNA microarray provides a new concept that the ratios of differentially expressed genes are magnified prior to detecting them. The ratio magnification is achieved with the integration of DNA reassociation and polymerase chain reaction (PCR) amplification and ensured with the design of the adapters and primers. The ADGE technique can be used either as a stand-alone method or in series with DNA microarray. ADGE is used in sample preprocessing and DNA microarray is used as a displaying system in the series combination. The combination of ADGE and DNA microarray provides a mutual complement of their strengths: the magnification of ratios of differential gene expression improves the detection sensitivity; the PCR amplification and efficient labeling enhance the signal intensity and reduce the requirement for large amounts of starting material; and the high throughput for DNA microarray is maintained.