After years of hope and frustation, research on artificial oxygen carr
iers seems to have exited from an apparent stagnation. Several product
s have recently been the subject of a certain publicity: one is a synt
hetic compound based on perfluorocarbons, while others are solutions o
f modified human hemoglobin (Hb). These latter transporters are prepar
ed from outdated bank blood or from recombinant Hb. Much progress have
been made in controlling the oxygen affinity of Hb solutions. Several
strategies, based on mutants or cross-links, have lead to Hb solution
s with properties similar to those of natural erythrocytes. The lack o
f the physiological effector 2.3-diphosphoglycerate in the purified Hb
solutions can be compensated for by a combination of mutations, or by
the type of crosslinking. Unfortunately, less progress have been made
to compensate the loss of the reducing system, and the rate of oxidat
ion may limit the useful lifetime of these solutions. A major obstacle
in the utilisation of the Hb based oxygen carriers (HBOC) is the appe
arance of a vasoconstriction, which may be overcome through a better u
nderstanding of the mechanism of interaction of NO with Hb. Apart from
this effect, the initial clinical tests have not revealed a toxicity
to the exposure of Hb solutions. There is thus some optimism that the
functional properties can be improved to produce a useful HBOC.