Dr Kiyoshi Nagai, a scientist at the U.K. Medical Research Council (MRC) Laboratory of Molecular Biology, Cambridge, holds a phial of human haemoglobin intended as a blood substitute. The need to develop a blood substitute has arisen because of increasing concern over contamination of blood stocks with viral & bacterial pathogens, such as HIV, the virus causing AIDS. The products of earlier attempts using recombinant DNA techniques on the bacteria Escherichia coli & Saccharomyces cerevisiae had proved toxic to the kidneys. This latest version, developed by scientists at the MRC & Somatogen Inc. in the U.S., has overcome this problem.