Gene discovery, i.e. detection of genes whose expression is affected in diseases or by different treatments of cells or animals, has become the focus of much genetic research. The technologies that are used to detect changes in expression level include polymerase chain reaction (PCR)-based subtraction methods, arrays of cDNA clones on chips or filters, serial analysis of gene expression, and differential display. In this paper we show that differential display can be used to investigate global gene expression in situations where a few genes change expression levels such as exposure of MCF7 cells to estradiol, and in more complex situations such as neuronal differentiation of human NTERA2 cells which affects a large number of genes. Furthermore, we show that differential display can replace Northern blotting and RNase protection as a tool to study the expression level of a specific gene in many samples. Results obtained by differential display can be stored in databases, where the identity of a band (gene or mRNA name) can be linked with information about the primer combination displaying the band and a gel image showing the band pattern, which is all the information that is needed to compare the expression level of this gene in other samples.