We are entering a new age in molecular genetics in which we can use expression data from microarray experiments to dissect cell, developmental and disease pathways more completely and more sensitively than ever before. Caenorhabditis elegans is the only animal model system with a complete genome sequence, and thus will have a key role in establishing approaches that make use of the full genome sequence. DNA microarrays could be used to identify genes that are regulated by programmed cell death pathways, specific transcription factors, specific cell-signalling pathways, expression of homologues of human disease genes in transgenic animals or addition of various pharmaceutical drugs. We have produced DNA microarrays that contain approximately 12,000 C. elegans genes (60% of the genome), and have nearly completed construction of full-genome microarrays containing over 19,000 genes. We have currently used the 12,000-gene microarrays in over 120 microarray experiments. In one set of experiments, we used a global approach to define 1,432 germline-enriched genes to illuminate the molecular basis for all of the germline-specific functions, including how the germ line remains totipotent and immortal.