Microarray studies have examined global gene expression in over 20 species of filamentous fungi encompassing a wide variety of research areas. The majority have addressed aspects of metabolism or pathogenicity. Metabolic studies have revealed important differences in the transcriptional regulation of genes for primary metabolic pathways between filamentous fungi and yeast. Transcriptional profiles for genes involved in secondary metabolism have also been established. Genes required for the biosynthesis of both useful and detrimental secondary metabolites have been identified. Due to the economic, ecological and medical implications, it is not surprising that many studies have used microarray analysis to examine gene expression in pathogenic filamentous fungi. Genes involved in various stages of pathogenicity have been identified, including those thought to be important for adaptation to the host environment. While most of the studies have simulated pathogenic conditions in vitro, a small number have also reported fungal gene expression within their plant hosts. This review summarizes the first 50 microarray studies in filamentous fungi and highlights areas for future investigation.