A study has been performed to evaluate the suitability of Vacutainer tubes in blood specimen collection for coagulation tests and to compare them with the conventional syringe technique employed in UK hospitals. Blood was collected from healthy volunteers, an ante-natal group and patients on long-term oral anticoagulants. Samples were stored at two different temperatures; 4 degrees C and ambient room temperature (RT). Prothrombin times, factor VII assays and APTT were performed at baseline and after 2 h and 4 h storage. There was significant activation of the extrinsic system in the blood samples collected by Vacutainer when stored at 4 degrees C which became more significant on prolonged storage. The effect was less pronounced when the Vacutainer tubes were stored at RT. In contrast, the blood collected by the syringe method did not show these changes with the exception of the ante-natal specimens where a lesser degree of activation than in the Vacutainer tubes was observed after 4 h at 4 degrees C. The activation of the Vacutainer samples at 4 degrees C is considered undesirable and could be of clinical significance in oral anticoagulant dosage.