Abstract: Many drug targets are components of complex signalling pathways, and in order to understand the true biological consequences of modulating these targets it is necessary to understand the biology of the system in great detail. Genomics research can contribute some of the tools to achieve this, for example through the use of cDNA microarrays. Since activation of signalling pathways leads to mRNA expression, microarray technology can be used to provide a detailed quantitative assessment of the consequences of this activation, often providing a completely new biological perspective on well established cellular systems. This review will discuss some of the results obtained using mRNA profiling of yeast and mammalian cells to analyse signalling pathways of relevance to inflammation and cancer, and will point towards the future applications of this exciting approach to drug target evaluation.