Hantavirus activity in rodents and human beings in Argentina has been known since the 1980's. In this study, we retrospectively investigated hantavirus infections among Argentine Hemorrhagic Fever (AHF) cases notified between 1987 and 1994, without virological confirmation. IgG and IgM antibodies to hantavirus were tested by ELISA. Among 1028 patients included in the study, we found 13 recent infections (1.26%) and 13 remote infections (1.26%). IgG antibodies determined in 745 healthy persons living in the same localities of recent infection cases, gave only one positive result (0.13%). Nine of the 13 recent infections had the clinical presentation of Hemorrhagic Fever with Renal Syndrome (HFRS) while the other four were in the form of Hantavirus Pulmonary Syndrome (HPS). We performed a clinical and epidemiological comparison between the nine patients with FHSR and two paired control groups: one with confirmed AHF and the other with Febrile Syndrome of Undetermined Etiology (FSUE), which were negative for hantavirus, Junin and LCM. There were no differences between clinical signs or symptoms. Nevertheless, normal or high leucocyte counts, with thrombocytopenia, hemoconcentration, high creatinine levels and proteinuria in HFRS cases resulted useful for differential diagnosis. These results showed the coexistence of Junin virus and hantaviruses in the endemic area of AHF, and indicate the importance of including the infection with these viruses in the differential diagnosis of hemorrhagic fevers and respiratory distress syndromes of unknown etiology. The clinical variability found could be related to the presence of more than one hantavirus serotype in our country.