Traffic noise was tested as a stress factor in an open-field study of urban and non-urban populations of two species belonging to the genus Apodemus: the striped field mouse and the yellow-necked mouse. The striped field mouse has inhabited green areas in cities for years, whereas the yellow-necked mouse was first observed in such areas relatively recently. Behavioral reactions to noise in the urban population of striped field mice were the same as the reactions observed in the non-urban population of the species. As for the yellow-necked mouse, behavior in response to noise in the non-urban population differed from that observed in the urban population. We see such differences as being related to the fact that striped field mice, which have inhabited urban areas for many generations, form a stable population in urban areas, and specific individuals are adapted to urban conditions. Yellow-necked mice, in turn, form no stable urban population and the individuals found in cities are most probably migrants, not adapted to urban conditions, which is the reason why their reaction to noise differs from the typical response.