Current guidelines on initial haemodynamic stabilization in shock states suggest infusion of either natural or artificial colloids or crystalloids. However, as the volume of distribution is much larger for crystalloids than for colloids, resuscitation with crystalloids alone requires more fluid and results in more oedema, and may thus be inferior to combination therapy with colloids. This chapter describes the currently available synthetic colloid solutions [i.e., dextran, gelatin and hydroxyethyl starch (HES)] in detail, and critically discusses their specific effects including potential adverse effects. Literature was selected from medical databases (including Medline and the Cochrane library), as well as references extracted from the available publications. Dextrans appear to have the most unfavourable risk/benefit ratio among the currently available synthetic colloids due to their relevant anaphylactoid potential, risk of renal failure and, particularly, their major impact on haemostasis. The effects of gelatin on kidney function are currently unclear, but potential disadvantages of gelatin include a high anaphylactoid potential and a limited volume effect compared with dextrans and HESs. Modern HES preparations have the lowest risk of anaphylactic reactions among the synthetic colloids. Older HES preparations (hetastarch, hexastarch and pentastarch) have repeatedly been reported to impair renal function and hemostasis, especially when the dose limit provided by the manufacturer is exceeded, but no such effects have been reported to date for modern tetrastarches compared with gelatin and albumin. However, no large-scale clinical studies have investigated the impact of tetrastarches on the incidence of renal failure in critically ill patients. When considering the efficacy and risk/benefit profile of synthetic colloids, modern tetrastarches appear to be most suitable for intensive care medicine, given their high volume effect, low anaphylactic potential and predictable pharmacokinetics. However, the impact of tetrastarch solutions on mortality and renal function in septic patients has not been fully determined, and further comparison with crystalloids in prospective, randomized studies is required. Such studies are currently ongoing and their results should be awaited before drawing final conclusions on the HES preparations.