BACKGROUND AND OBJECTIVES: The aim of this work was to study the incidence of transfusion-induced platelet-reactive antibodies in a selective patient population and evaluate different methodologies for platelet antibody screening (PAS). MATERIALS AND METHODS: The patients were retrospectively selected and divided into three separate groups: haematological malignancies (Group 1: n = 33); cardiac and orthopaedic patients (Group 2: n = 31) and a control group (Group 3: n = 23) selected with the same diagnoses of Group 2. PRE- and POST-transfusion samples were tested for PAS by the following tests: PIFT (platelet immunofluorescence test), MAIPA (monoclonal antibody immobilization of platelet antigen), Flow PRA(R) and LCT (lymphocytotoxicity test). RESULTS: There was not a 100% concordance among the methodologies used. PIFT, MAIPA and Flow PRA presented very similar results whereas that of LCT differed from the other methods. A high rate of positive results (32%) was found in the PRE samples followed by an increase of almost 50% after blood transfusion (POST samples: 42.5% of positivity), but there was a statistical difference (P < 0.05) between the PRE and POST transfusion sample only for the Flow PRA(R) technique tested on Group 2. Human leucocyte antigen (HLA) class I antibodies were present on 97.4% of POST positive samples, 5.4% presented anti-human platelet antigen (HPA)-1b antibodies and 8.1% presented a mix of pan-reactive antibodies against glycoprotein IIbIIIa, IaIIa and IbIX. CONCLUSIONS: Blood transfusion did not increase the rate of alloimmunization in our haematological patients (Group 1); however, the patients were already admitted with a high rate of alloimmunization (12%). Group 2 patients are being immunized and the impact of this procedure remains to be studied as these patients may eventually undergo further hospitalization and receive more blood transfusion.