We investigated the influence of exposure to chronic salinity (NaCl) and mifepristone (a glucocorticoid antagonist) for 24 d on corticosterone release rates (baseline, stress-induced and corticosterone increase) of Northern Leopard Frogs (Rana pipiens). The dataset contains per-individual, per-day values for snout-vent length (mm), wet mass (g), developmental stage (Gosner stage), log-transformed corticosterone release rates (baseline, stress-induced, and corticosterone increase; pg/h), and mass-corrected and log-transformed release rates (pg/g/h). It also contains coefficients of determination (%) for each corticosterone release rates calculated following quantification with enzyme immunoassays. Within the dataset, 'Died' indicates if that larvae subsequently died in the experiment