Identifying changes in gene expression is of prime interest in molecular biology. A variety of methods have been developed for analyzing differentially expressed genes. Among these techniques, differential display reverse transcription PCR (DDRT-PCR), representational difference analysis (RDA) and suppression subtractive hybridization (SSH), which were based on differentially screening and subtractive hybridization technology, are applied most widely. Gene chips (gene microarrays) for analyzing gene expression patterns on larger-scale had also been developed. Here we present a review of these methods.