Serum samples from 43 patients with haemorrhagic fever with renal syndrome (HFRS) were detected with a haemagglutination–inhibition test for serotyping hantavirus-specific IgM antibody; 35 patients were positive to the Apodemus agrarius (wild rat) serotype, eight were positive to non-types and none were positive to the house rat type. A. agrarius serotype was detected in the winter. Thus, serotyping of HFRS antibody would be helpful to identify the source of hantavirus infection, enabling an early diagnosis, followed by prevention and cure.