Samples of blood, spleen and legs from 112 culled roe deer (Capreolus capreolus) were collected from nine sites widespread in the United Kingdom. The prevalence of infection with Ehrlichia phagocytophila was determined by serology and polymerase chain reaction. Means of 58% of 102 plasma or serum samples were seroreactive by IFA, 38% of 84 blood samples and 29% of 82 spleen samples were positive by PCR. Ticks on legs of 71 roe deer were Ixodes ricinus larvae, nymphs and adults and 83% of legs were infested. Numbers of ticks corresponded positively to the percentage of samples positive for E. phagocytophila by serology and PCR for different sampling sites. Ixodes ricinus nymphs collected from the vegetation at one site with infected deer were analysed for infection with E. phagocytophila by examination of Feulgen stained salivary glands. Of 135 nymphs 5% were infected. These results confirm that roe deer are commonly parasitized by both E. phagocytophila and its vector tick in such a way that it is likely to be an important natural mammalian reservoir of E. phagocytophila.