The method of sample collection and time interval from venipuncture to test performance is considered to be important in platelet function testing. Platelet function studies can be performed in whole blood with the use of an impedance lumi-aggregometer, and an examination of the influence of these variables on the outcome of such a study is important. Twelve healthy donors had blood drawn with the use of conventional approach for platelet function testing and a Vacutainer method. Platelet function studies were performed at three time points over a three-hour period. No significant differences in results were observed between the methods of collection and the time to test performance. It is concluded that for platelet function screening in whole blood, with the use of an impedance lumi-aggregometer, a Vacutainer sample maintained at room temperature and tested within three hours is satisfactory.