1. The technique for seeding eggs for the propagation of neurotropic horsesickness virus in the developing chick embryo is described in detail. 2. It is found that the virus retains its neurotropic character and multiplies in the brain of the embryo; little if any multiplication takes place on the chorio-allantoic membrane or in the body of the embryo. 3. 'I'he titre of the virus reaches a peak after 4-5 days incubation at 37° C. after which there is a progressive fall in virus content; after 8 days only traces of virus are detectable. 4. The virus produces no macroscopically detectable lesion on the membrane and only slight heamorrhagic infiltration in the brain. 5. The virus exerts no specific lethal action on the embryo. Several chicks have hatched and were found to retain no virus in the brain. 6. The embryo mortality ratio amongst seeded eggs during the first 5 days of incubation does not exceed 4 per cent. 7. The possibility of using the chick embryo method for the propagation of virus for vaccine production is discussed.