Experiments are described which were designed to examine the possibility that death of the goat × sheep hybrid foetus is due to the passage of haemolytic antibody from mother to foetus. 'Naturally occurring' haemolytic antibodies to sheep red cells were found in the sera of some goats with normal or hybrid pregnancies. 'Heterologous' anti-bodies, considered to be of the immune type, were found in some but not all goats with hybrid foetuses; these 'heterologous' antibodies were not found in goats carrying goat foetuses. No immune globulins of maternal or foetal origin were found in foetal plasma or in allantoic or amniotic fluids. No real evidence was obtained for the presence of immune globulins on the red cells of hybrids whether or not their mothers had anti-sheep haemolysins in their sera. It is concluded that haemolytic antibodies are not responsible for the death of the goat× sheep hybrid foetus.
The electrophoretic pattern of hybrid haemoglobin was examined.