The numbers of Ixodes ricinus (L.) and Dermacentor reticulatus (Fabricius) larvae and nymphs attached to small mammals are influenced by interspecific competition.The present study analyses data collected over several years in two study areas: Kosewo Górne (Mazurian District, N Poland; between July 1997 and July 2009) and Białowieża Primeval Forest (E Poland; in July 2007). In total, 975 ticks were collected from striped field mice (Apodemus agrarius), yellow-necked mice (A. flavicollis), bank voles (Myodes glareolus), and root voles (Microtus oeconomus). In total, of the 203 investigated rodents, 137 were infested with ticks and 39 demonstrated mixed infection. The numbers of the two tick species found on Apodemus mice were significantly negatively correlated with those on root voles; similarly, although bank voles were significantly more frequently infested by I. ricinus than by D. reticulatus, the reverse was observed in root voles. In addition, among the voles, each tick species was found in different locations on the host body, which could also result from competitive interactions; furthermore, competitive release regarding microhabitat selection was observed on hosts infested with one tick species.This competition may be driven by the limited area of host body available for foraging by ticks, i.e., safe areas of high vascularization covered by thin skin. However, the mechanisms of such competition require further investigation.