Because detritus is a poor quality food resource, nutrient enrichment can increase detrital quality with subsequent effects on higher trophic levels.  Fine (<1 mm) and coarse fractions of organic matter (>1 mm) have characteristically different microbial assemblages: fungi dominate coarse fractions and bacteria dominate fine fractions.  Thus, determining how nutrient enrichment effects differ between fine vs. coarse particulate organic matter fractions is important in increasing our ability to predict nutrient enrichment effects in a variety of systems.  We examined nutritional quality (C:N and C:P), microbial biomass, and microbial activity (respiration) associated with fine and coarse particulate organic matter in two southern Appalachian headwater streams, one receiving long-term nitrogen and phosphorus enrichment, at the Coweeta LTER site, NC, USA.  We predicted relatively greater changes in coarse vs. fine material in the enriched stream because of the importance of fungi in these headwater streams, which dominate coarse fractions and respond positively to increased nutrient availability.  Nutrient enrichment had a significant effect on resource quality, via differences in microbial mass and activity as well as carbon:nutrient ratios.  This response suggests that coarse particulate organic matter and its associated consumers may be a key pathway by which nutrients affect detritus-based systems.