Nutrient diffusing substrates (NDS) are important tools for evaluating periphyton nutrient limitation in aquatic systems.  Streams studied with NDS can have water temperatures that vary seasonally from 0^o to over 20^o C.  If NDS diffusion rates vary with water temperature, it could be difficult to compare studies performed at different times of year.  In addition, there is frequently little consideration given to the nutrient concentration used when designing NDS studies, which could further impact nutrient diffusion rates.  We tested diffusion rates for nitrogen (N) and phosphorus (P) NDS vials at three concentrations (0.05, 0.1, and 0.5 mol/L) and three temperatures (4, 15 and 21°C) throughout a 21 day period in environmental chambers.  Mean diffusion rates varied by concentration, however, they did not vary with temperature. As observed in previous studies, N and P diffusion rates were greatest initially when nutrient concentrations were greatest, and declined for the duration of the 21 day period.  P diffused more quickly than N at all temperatures and concentrations.  Our results indicate that stream water temperature does not likely influence NDS diffusion rates.  However, researchers should carefully consider the nutrient concentration used when planning nutrient limitation studies using NDS.