The dauer is a developmental stage in C. elegans that exhibits increased longevity, stress resistance, nictation and altered metabolism compared with normal worms. We have used DNA microarrays to profile gene expression differences during the transition from the dauer state to the non-dauer state and after feeding of starved L1 animals, and have identified 1984 genes that show significant expression changes. This analysis includes genes that encode transcription factors and components of signaling pathways that could regulate the entry to and exit from the dauer state, and genes that encode components of metabolic pathways important for dauer survival and longevity. Homologs of C. elegans dauer-enriched genes may be involved in the disease process in parasitic nematodes.