In the present paper the author refers the experiments made by the inoculation of the influenza virus, PR8 strain, passages 581 to 735, in 151 pregnant or mated hamsters. He observed alterations in some embryos and foetuses and isolated the virus from them and from the normal baby hamster. The inoculation were made by parenteral and nasal routes. The virus was isolated from adult hamsters, baby hamsters, foetuses and embryos in 55 per cent of cases. There was 15,2 per cent of foetal or embryonic alterations.