New high-throughput screening technologies have led to the identification of hundreds of genes with potential roles in cancer or other diseases. For evaluation of promising candidate genes, however, in-situ analysis of high numbers of clinical tissue samples is mandatory. The tissue microarray (TMA) technology greatly facilitates such analysis. In this method minute tissue samples (0.6 mm in diameter) from up to 1000 different tissues can be analyzed on one microscope glass slide. All in-situ methods suitable for histological studies can be applied to TMAs without major changes in protocols, including immunohistochemistry, fluorescence in-situ hybridization, or RNA in-situ hybridization. Because all tissues are analyzed simultaneously with the same batch of reagents, TMA studies provide an unprecedented degree of standardization, speed, and cost efficiency.