We report a patient with a variant of Alport's syndrome: macrothrombocytopenia, leucocyte inclusions, deafness and proteinuria. Ultrastructural studies revealed giant spheroid platelets with a high density of organelles and a disorganized microtubular system. In addition, Fechtner inclusions were observed in neutrophils of the patient and her mother. In platelet rich plasma platelets aggregated normally for the low platelet number, although no shape change was visible. Platelet studies in whole blood using impedance aggregometry gave supernormal aggregation curves; this is not in agreement with the abnormally long bleeding time, showing the limited usefulness of this technique in patients with such large platelets. The megakaryocytes (MK) showed two different distribution patterns of the demarcation membrane system (DMS), which may explain the production of few large platelets. The formation of platelets occurred by fragmentation of the granular zone of the MKs, which seemed to be followed by expulsion of platelets through openings of the peripheral zone. The involvement of cytoskeletal structures in the organization of the DMS and the expulsion of platelets is discussed.