Use of intravenous immunoglobulins (IVIGs) is a well-established therapy in patients with acute or chronic autoimmune thrombocytopenic purpura (ITP). The aim of the present open, prospective study was to investigate efficacy and safety of the novel IVIG preparation BT681 (Biotest Pharma GmbH, Dreieich, Germany) in adult patients with chronic ITP (cITP). In order to fulfil high standards of purity and viral safety, an additional HPLC step has been introduced and validated virus removal and inactivating procedures are included in the manufacturing process of BT681. A total of 24 patients with platelet counts between 3/nl and 27/nl received a total dose of 2 g/kg body weight BT681 in standard dosage regimens: 1.0 g/kg/day for 2 days in 15 patients and 0.4 g/kg/day for five consecutive days in nine patients. Platelet response (platelet count > or =50/nl) and regression of haemorrhages were documented during the 28 days study period and safety parameters including adverse events, laboratory investigations and vital signs were regularly monitored. The overall response rate was 91.7%, that is 22/24 patients responded to BT681 treatment. The median time to platelet response was 3.0 days, the duration of response 25.5 days; the median max. platelet count 222/nl and the time to max. platelet count 7.5 days. During the entire observation period, platelet counts below baseline were only observed in five responders; in half of the patients, platelet counts were even above 50/nl at the end of follow-up. Corresponding to the good platelet response, the clinical symptoms improved markedly in the majority of patients within the first week after start of BT681 infusions with 88.9% overall regression of haemorrhages in comparison with baseline. The evaluation of platelet parameters showed a slight tendency in favour of the 5 days group, evaluation of haemorrhage severity slight advantages for the 2 days group. The adverse event data indicate that the therapy with BT681 was safe and well tolerated in both treatment groups even if minor effects were more frequent in patients treated with the 2 days regimen. The large majority of adverse events were known intolerabilities during the treatment phase described as mild and transient. The results demonstrate that the new immunoglobulin preparation BT681 is effective and safe in the treatment of adult patients with cITP.