2D polyacrylamide gel electrophoresis has been the traditional workhorse of proteomics, allowing for the resolution of several thousand proteins in a single gel. Difference gel electrophoresis is an emerging technology that allows for accurate quantification with statistical confidence while controlling for nonbiologic variation, and also increases the dynamic range and sensitivity of traditional 2D polyacrylamide gel electrophoresis. With inclusion of an internal standard formed from equal amounts of every sample in an experiment, difference gel electrophoresis technology also allows for repetitive measurements and multivariable analyses to be quantitatively analyzed in one co-ordinated experiment, yielding statistically-significant changes in protein expression related to many disease states. This technique promises to be an important tool in clinical proteomics and the study of the mechanism of disease, investigating diagnostic biomarkers and pinpointing novel therapeutic targets.