Hantaviruses which are the members of Bunyaviridae, differ from other members of this family since they are transmitted to humans by rodents. More than 200.000 cases of hantavirus infections are reported annually worldwide. Hantaviruses can lead to two different types of infection in humans, namely, hemorrhagic fever with renal syndrome (HFRS) and hantavirus pulmonary syndrome (HPS). HFRS is the most common type of hantavirus infection in Europe and Asia and the most common virus types are Dobrava, Puumala, Hantaan and Seoul. A total of 25 hantavirus suspected cases have been reported from the Western Black Sea region of Turkey and 12 of these were confirmed serologically as "Puumala" subtype. Serological tests such as indirect immunofluorescence assay (IFA), are used for diagnosis and typing of the hantaviruses, however, since cross-reactions are common between the subtypes, the results of these tests should be confirmed by other methods. In this report two cases with hantavirus infection defined serologically were presented. Two male patients, 55 and 50 years old, respectively, living in Giresun province of Eastern Black Sea region, Turkey, were admitted to the State Hospital with the complaints of fever, sweating and diarrhoea without blood or mucus. Since thrombocytopenia and renal failure were detected in these two cases, they were transferred to the University Hospital. Presence of fever, thrombocytopenia and renal failure, with no laboratory findings of a bacterial infection and no growth of microoorganisms in the clinical specimens, admittance of the patients during summer and history of being present in the fields, necessitated to rule out leptospirosis, Crimean Kongo hemorrhagic fever and hantavirus infection which were all endemic in our area. Further investigation of the serum samples at the National Reference Virology Laboratory by IFA (Hantavirus Mosaic-1, Euroimmun, Germany) revealed hantavirus IgM and IgG antibodies >= 1:100 titer and the results were confirmed by immunoblot test (Hantavirus Profile 1 EUROLINE IgG and IgM, Euroimmun, Germany). Hantavirus Dobrava subtype was determined in both of the cases. Reverse transcriptase real-time PCR (Hantavirus Renal Syndrome General-type I&II Real Time RT-PCR; Shanghai ZJ Bio-Tech, China) revealed negative result. The first case was discharged with complete cure, however, the second case died. These cases which were the first cases from the Eastern Black Sea Region emphasized that hantavirus infections should be taken into consideration in patients presenting with fever, thrombocytopenia and renal function disturbance.