Nutrient uptake is a key ecosystem process that results in the reduction and transformation of available nutrients at a site. Decades of laboratory and field experiments have shown that nutrient uptake is dynamic with concentration of that nutrient. Stoichiometric theory suggests that uptake of a nutrient should also be related to the availability of other key nutrients, but to date little work has been done in this research area. We investigated the stoichiometry of uptake across wide ranges in concentrations and ratios of nitrate (NO3-) and phosphate (PO43-) by conducting independent NO3-, PO43-, and dual NO3- + PO43- slug injections in three streams in the West Fork of the Gallatin River watershed in August 2010. The individual additions of NO3- and PO43- each resulted in Michaelis-Menten uptake kinetics across the observed concentration range in all three streams. During the dual slug, uptake rates of each nutrient increased with the addition of the second nutrient, suggesting co-limitation by these two nutrients at all sites. The absolute and relative magnitudes of these increases in NO3- and PO43- uptake varied between sites, however, suggesting that these sites vary in the relative strengths of nitrogen (N) versus phosphorus (P) limitation. We present these results in the context of inter-site variations in epilithic N:P ratios to highlight the role of coupled N and P dynamics in controlling nutrient uptake and resulting patterns of nutrient availability in streams.