HAEMOGLOBIN HAS THE PROPERTY OF REVERSIBLE OXYGENATION AND IS THE RESPIRATORY PIGMENT OF BLOOD. SOLUTIONS OF HAEMOGLOBIN OR MODIFIED HAEMOGLOBIN HAVE BEEN INVESTIGATED AS BLOOD SUBSTITUTES. THERE ARE. HOWEVER, RESERVATIONS CONCERNING HAEMOGLOBIN SOLUTIONS AS BLOOD SUBSTITUTES: BLOOD ITSELF MUST BE AVAILABLE FOR THEIR PRODUCTION, AND THERE IS ALSO CONCERN ABOUT IMPAIRMENT OF IMMUNE MECHANISMS. THE RECENT PRODUCTION OF RECOMBINANT HUMAN HAEMOGLOBIN MAY OVERCOME THESE PROBLEMS.