We have compared the effects of progressive in vitro haemodilution (30% and 60%) with potato starch derived hydroxyethyl starch and corn starch derived hydroxyethyl starch on blood coagulation in 80 patients using thrombelastography. Both solutions significantly compromised blood coagulation as evidenced by an increase in coagulation time and decrease in angle alpha, maximum amplitude and coagulation index (p < 0.05). Blood coagulation was more compromised during haemodilution with potato starch derived hydroxyethyl starch as compared with corn starch derived hydroxyethyl starch (p < 0.05). When taking the effect of haemodilution with 0.9% saline into account, haemodilution with both hydroxyethyl starch solutions also augmented clot lysis (p < 0.05), with potato starch derived hydroxyethyl starch having a greater effect than corn starch derived hydroxyethyl starch (p < 0.05). We conclude that potato starch derived hydroxyethyl starch compromises in vitro blood coagulation more than corn starch derived hydroxyethyl starch.