The present article aims to present the current state of knowledge on methods for the functional characterization of genes. Progress in the analysis of gene expression in cells or tissues of whole is indisputable and contributes to increased understanding of the role of individual genes. The use of traditional methods of functional analysis of genes, such as the method of prediction by homology, the method of inactivation, and increased expression of genes is increasingly being replaced by a strongly enhanced tools on bioinformatics analysis of microarrays and DNA chips. In a practical way of knowledge about the features and changes in gene expression is used in medical diagnostics, pharmaceutical industry and biotechnology of plants and animals.