BACKGROUND: Sometimes we receive specimens collected several hours ahead, hemolyzed, or turbid. To decide to analyze the samples or not, the influence of storage time, hemolysis, and turbidi-ty on PT and PTT were studied. METHODS: Total of 198 cases for PT and 192 for aPTT were studied to clarify the effect of storage time on PT and aPTT. We performed the tests of PT and aPTT at 0, 2, 4, and 8 hours after collection of specimens. For the hemolysis effect study, we used 31 cases. Slightly, moderately, and severely hemolyzed plasma were obtained by adding hemolysate to plasma. For the turbidity effect study, we used 30 cases. Slightly, moderately, and severely turbid plasma were obtained by adding Intrali-pos (20% soybean oil) to plasma. RESULTS: Delayed test time affected the aPTT results after 8 hours. Hemolysis affected the PT and aPTT results. Turbidity did not affect the PT and aPTT results; however, the Coagrex-100s rejected to analyze the severely turbid samples. CONCLUSIONS: It is recommended that specimens be evaluated immediately or within 4 hours and that hemolysed or severely turbid specimens for PT and aPTT tests not be used.