Dusky-footed wood rats, Neotoma fuscipes,have been implicated in the natural maintenance of Ehrlichia phagocytophilasensu lato, the agent of human granulocytic ehrlichiosis (HGE), in northern California based on high seroprevalence and amplification of E. phagocytophilas.l. DNA from wood rat blood. In order to further assess granulocytic ehrlichiosis in wood rats, we examined wild-caught wood rats for infection and then performed experimental intra-peritoneal infections with E. phagocytophilas.l. in horse or wood rat blood, and tested animals for 120 days by polymerase chain reaction (PCR) and serology. Of 15 wood rats collected from northern California, three were antibody and PCR-positive for E. phagocytophilas.l. at the time of capture. The naturally infected wood rats remained PCR-positive for a mean of 52 days (±7 SD). Experimental IP passage of E. phagocytophilas.l. in wood rat blood was successful in three of four wood rats and the mean duration of PCR-positivity was 75 days (±21.2 SD). Experimental infection with E. phagocytophilas.l. in horse blood succeeded in all four of the recipients and the mean duration of PCR-positivity of 81 days (±17.5 SD). No infected individual appeared to be ill based on feeding behavior, activity, and hydration status. These data confirm that wood rats are susceptible to E. phagocytophilas.l., may develop prolonged infection without clinical ehrlichiosis, and may play a role in maintaining E. phagocytophilas.l. in nature.