The incidence of acquired inhibitors against clotting factors is rare in previously healthy subjects. Most of them are related to underlying autoimmune diseases or postpartum state. We report a case of acquired postpartum bleeding disorder in a non-haemophilic patient caused by an inhibitor of the intrinsic pathway that affected factor IX and the response to treatment with recombinant factor VIIa (rFVIIa; NovoSeven, Novo Nordisk, Denmark) and prednisone. A 39-year-old woman without previous history of bleeding disorders was admitted as a result of the recent appearance of skin haematomas in upper and lower extremities. The patient had delivered her third child 1 month before without significant bleeding, requiring analgesic treatment with Diclofenac and Aspirin for 10 d. Initial laboratory data showed normal blood counts and biochemistry. A plasma coagulation study disclosed a prolonged activated partial thromboplastin time (aPTT) of 76·8 s (ratio 2·7) and normal prothrombin time, thrombin time, fibrinogen level and platelet aggregation. While other coagulation tests were being carried out, the patient developed an haemarthrosis at her right elbow with signs of compartment syndrome. Clotting factors assay revealed a decreased factor IX (40 µ/dl), factor XI to be on the lower limit of normal range (61 µ/dl), and normal factors II, VIII, X, XII, XIII and von Willebrand factor. No alterations in d-dimer levels were observed (173 ng/ml), and functional tissue type plasminogen activator (t-PA) and α2-anti-plasmin were barely increased. Screening and confirmation tests for lupus anticoagulant were negative. The aPTT and factor IX levels were hardly corrected after mixing with control plasma, indicating the presence of an inhibitor that showed no time dependence. New mixtures with normal pooled plasma showed the presence of an inhibitor against factor IX (2·5 Bethesda units). Treatment with rFVIIa 90 μg/kg/4 h and prednisone 1·5 mg/kg/24 h was started, resulting in rapid recovery of factor IX levels. However, the prolongation of aPTT persisted, requiring 15 infusions of rFVIIa to achieve the complete disappearance of the clinical picture. Table I shows the patient's coagulation data at admission and during the treatment period. A prospective study of 100 consecutive cases with prolonged aPTT of unknown aetiology identified the presence of lupus anticoagulant as the most common cause (Kitchens, 1988). Alterations of clotting factors in the intrinsic pathway may also be responsible for the prolongation of the aPTT. In the present report, a postpartum-acquired inhibitor of the intrinsic pathway affecting factor IX was detected. The presence of an acquired factor IX inhibitor is infrequent in haemophilia B patients and is extremely rare in non-haemophilic patients (Feinstein, 1995). A literature search identified reports of acquired factor IX inhibitors in a patient with autoimmune disease, two children and a patient with adenocarcinoma of the colon. Bleeding in patients with acquired haemophilia is often severe, even with low titres of inhibitor, especially during the first weeks after presentation. However, the presence of a functional factor IX of 40 µ/dl seems insufficient to cause such prolongation of the aPTT. This suggests that other components of the intrinsic pathway may be affected, although the determination of other clotting factors showed no significant alterations. The aims in the treatment of acquired haemophilia are control of the haemorrhage and elimination of the autoantibody. rFVIIa has proven effective in patients with alloantibodies and autoantibodies against factor VIII or IX (Lusher, 1996; Negrier & Hay, 2000). In a NovoSeven compassionate-use programme in 38 patients with acquired autoimmune depletion of factor VIII (Hay et al, 1997), a median of 28 doses were administered per episode. In this case, 15 infusions were required to achieve a complete clinical response. Remarkably, d-dimer did not increase significantly during the treatment with rFVIIa. Persistence of the prolongation of the aPTT, despite recovery of normal factor IX levels during treatment with rFVIIa, supports the hypothesis of an inhibitory action against other factors involved in the intrinsic pathway. Another explanation could be interference between the presence of large amounts of factor VIIa and the determination of factor IX. Spontaneous disappearance of postpartum-acquired inhibitors has been reported. However, owing to the severity of the bleeding, our patient started treatment with prednisone, which was maintained with tapered doses for 4 months. After discontinuation of immunosuppresive therapy, factor IX levels and aPTT remain between normal ranges.