This randomised double blind prospective study compared the effective intravascular volume expansion and maintenance, with two types of starches following induced haemorrhagic hypovolaemia. Twenty healthy male volunteers aged between 18 and 65 year were bled 10% of their total blood volume in fully monitored conditions and under the supervision of a trained specialist doctor and research nurse. The lost blood volume was replaced using one of the starch solutions. Effective intravascular volume expansion was monitored hourly using the (51)Cr radio-labelled red blood cell dilution technique, we compared the effects of two hydroxyethyl starch colloid preparations, one a high molecular weight and the other a low molecular weight preparation, on the plasma volume changes over time. The large molecular weight starch (Hextend) provided a less well-sustained volume expansion effect than the smaller one (Voluven)