Distribution of Necromys lactens and Phyllotis osilae (Rodentia: Cricetidae: Sigmodontinae) in northwestern Argentina: predictive models based on the concept of ecological niche. We used presence data from field records, museum specimens and literature sources to model the potential distribution of two species of sigmodontine rodents, Necromys lactens and Phyllotis osilae in northwestern Argentina, based on environmental variables. We used the DOMAIN program, which based on presence data defines the environmental space that imposes conditions to the species distribution. We worked with two data sets, one constituted only by reliable data and the other one constituted by these reliable data plus other information considered more doubtful because of its controvertible identification and location. The models obtained from the reliable data set were more efficient in the prediction of distribution than doubtful data, with Kappa index of 0.69 and 0.63 for Necromys lactens and Phyllotis osilae, respectively. These results indicate that both species are restricted to the upper portions of the most important mountains in the region and that their distribution consists of islands or patches immerse in a complex matrix of forest and semi-desert environment. Both species were associated to high altitude grasslands and ecotone environments between 1200 and 3200 m elevation, being P. osilae‘s distribution a little more extended than N. lactens.