Hemorheological results may be influenced by the time between blood sampling and measurement, and storage conditions (e.g., temperature, time) during sample delivery between laboratories may further affect the resulting data. This study examined possible hemorheological alterations Subsequent to storage of rat and dog blood at room temperature (22 degrees C) or with cooling (4 similar to 10 degrees C) for 2, 4, 6, 24, 48 and 72 hours. Measured hemorheological parameters included hematological indices, RBC aggregation and RBC deformability. Our results indicate that marked changes of RBC deformability and of RBC aggregation in whole blood can occur during storage, especially for samples stored at room temperature. The patterns of deformability and aggregation changes at room temperature are complex and species specific, whereas those for storage at the lower temperature range are much less complicated. For room temperature storage, it thus seems logical to Suggest measuring rat and dog cell deformability within 6 hours; aggregation should be measured immediately for rat blood or within 6 hours for dog blood. Storage at lower temperatures allows measuring EI up to 72 hours after sampling, while aggregation must be measured immediately, or if willing to accept a constant decrease, over 24 similar to 72 hours.