Prophylactic platelet administration is indicated at counts below 20×109/1. The bleeding tendency and severity were compared between thrombocytopenic patients with acute-lymphocytic leukemia (ALL) and acute non-lymphocytic leukemia (ANLL) in the ranges of 10–20×109/1 platelets, while prophylactic platelet administration was given only below 10×109/1. The bleeding tendency for ALL was quite similar at platelet counts above or below 10×109/1. The bleeding tendency was significantly lower (p<0.001) when the platelets were above this level in ANLL patients. When the thrombocytopenia was caused by chemotherapy, the bleeding was significantly lower in both types of leukemia above 10×109/1 (p<0.05 for ALL, p<0.001 for ANLL) as compared with lower counts. When the thrombocytopenia was caused by leukemia, the bleeding tendency was similar in both types of leukemia and at all platelet counts (below 20×109/1). Fever, not associated with sepsis, augmented the bleeding severity of patients with ANLL. Stable or rising counts of platelets were associated with significantly lower bleeding tendency above 10×109/1 only in ANLL patients. The decision for prophylactic platelet administration at counts below 20×109/1 should be guided by the type of the leukemia (ALL vs. ANLL), the cause of throm-bocytopenia (chemotherapy vs. leukemia per se), the trend of the platelet counts, presence of fever and patient's age (below or above 18 years). Prophylactic platelet administration can be safely postponed until the count is below 10 × 109/1 in paitents with ANLL, without fever, with chemotherapy-induced thrombocytopenia and older than 18 years, regardless of the platelet trend.