To find out if Hantavirus infection, as a cause of acute renal failure, has been overlooked in the past. To determine if Hantavirus can be found in wild rodents, particularly in red bank voles (Clethrionomys glareolus), living in the area.General hospital, Twente area.Retrospective selection of patients, hospitalised between 1970 and 1989 with renal failure due to biopsy-proven or clinically probable acute interstitial nephritis of unknown aetiology. Sera from the acute phase of the disease, if still available, or sera taken in 1989 were tested for anti-Hantavirus antibodies. Red bank voles, trapped in the area were tested for Hantaviral antigen and specific antibodies.Out of 12 patients, 10 could be investigated. Anti-Hantavirus antibodies were detected in 5 patients. All patients had very probably acquired the infection in the Twente area. In 4 of 10 red bank voles Hantaviral antigen and specific antibodies were found.The findings suggest that Hantavirus infections have been occurring in this area over a long period of time and are underdiagnosed.