SUMMARYPrevalence and abundance ofBartonellaspp. infections were studied over a 3-year period in woodland and grassland rodents in North-Eastern Poland. Prevalence of bacterial infections was similar in the two rodent communities, with one leading host species in each habitat (46·3% inApodemus flavicollisversus 29·1% inMyodes glareolusin forest, or 36·9% inMicrotus arvalisversus 13·7% inMi. oeconomusin grassland). Prevalence/abundance of infections varied markedly across the 3 years with 2006 being the year of highest prevalence and abundance. Infections were more common during autumn months inMy. glareolusandA. flavicollis, and in juvenile and young adult (age classes 1 and 2)My. glareolusandMi. oeconomusthan in adults (age class 3). Higher prevalence and abundance ofBartonellainfections were found in maleA. flavicollisin comparison to females. These data are discussed in relation to the parasite genotypes identified in this region and with respect to the role of various ecological factors influencingBartonellaspp. infections in naturally infected host populations.