Although the effectiveness of hydroxyethyl starch (HES) as a cryoprotectant for human red blood cells (HRBC) is well known, no clinical application has evolved so far. In contrast to glycerol HES has the advantage of causing no hemolysis per se. This offers the opportunity of a one-step procedure without a time consuming postthaw washing procedure prior to transfusion. In this study the in vitro results obtained with red blood cells from 8 dogs (DRBC) are reported and compared to HRBC (n = 5). It turned out that DRBC had a similar 2,3-DPG and a lower ATP content. Postthaw survival in terms of saline stability differed markedly (67 +/- 6 and 86 +/- 2%, respectively). DRBC were more susceptible to hypotonic stress than HRBC. Nevertheless, after cryopreservation 91% (HRBC) and 92% (DRBC) of the original 2,3-DPG were found in the thawed RBC concentrates.