Stoichiometric relationships between consumers and resources in detritus-based ecosystems have received little attention, despite the importance of detritus in most food webs. We analysed carbon (C), nitrogen (N), and phosphorus (P) content of invertebrate consumers, and basal food resources in two forested headwater streams (one reference and the other nutrient-enriched). We found large elemental imbalances between consumers and food resources compared with living plant-based systems, particularly in regard to P content, which were reduced with enrichment. Enrichment significantly increased nutrient content of food resources (consistent with uptake of N and P by detritus-associated microbes). P content of some invertebrates also increased in the enriched vs. reference stream, suggesting deviation from strict homeostasis. Nutrient content varied significantly among invertebrate functional feeding groups, orders and, to some extent, size classes. Future application of stoichiometric theory to detritus-based systems should consider the potential for relatively large consumer-resource elemental imbalances and P storage by insect consumers.