Elimination of unwanted side-effects, especially transfusion-transmitted diseases (HIV and hepatitis) and leucocyte-mediated allosensitisation, is an important goal of modern transfusion medicine. The problems and high cost factor involved in collecting and storing human blood and the pending world-wide shortages are the other driving forces contributing towards the development of blood substitutes. Two major areas of research in this endeavour are haemoglobin-based oxygen carriers (HBOCs) and perfluorochemicals. Even though they do not qualify as perfect red blood cell substitutes, these 'oxygen carrying solutions' have many potential clinical and non clinical usages. These can reach tissues more easily than normal red cells and can deliver oxygen directly. These are not without adverse effects, and extensive clinical trials are being conducted to test their safety and efficacy. New understandings on the mode of action of these products will help to define their utility and application. Only after successful clinical trials can they be used for patient management, after approval by the FDA. MJAFI 2003; 59 : 45-50Key Words : Blood substitute; Haemoglobin solutions; Perfluorocarbons main advantages include availability in large volumes, storage for prolonged periods, rapid administration (without typing and cross matching) and sterilisation by pasteurisation. Their main known disadvantages are, reduced circulation half-life, haemodynamic and gastrointestinal perturbations, probably related to nitric oxide (NO) scavenging, free radical induction, and alterations of biochemical and haematological parameters (increase in liver enzyme levels, platelet aggregation) [1][2][3]. Purified haemoglobin solutionsThe first step in the pursuit for red cell substitute was