Summary The colloid and crystalloid solutions used for resuscitation should preferably be free from effects on coagulation. In 10 volunteers, the effects of haemodilution with various concentrations of 0.9% sodium chloride and 4% succinylated gelatin were assessed by Sonoclot analysis, which describes the whole coagulation process. Small and moderate haemodilution (up to 40%) with 0.9% sodium chloride promoted coagulation. Similar haemodilution with 4% succinylated gelatin impaired coagulation, and at 60% haemodilution coagulation was very poor. These findings need to be confirmed in vivo and their clinical relevance determined.