Conservative flocks are usually small populations in which inbreeding and mutations may result in unfavourable changes. With this aim, studies were conducted on the karyotypes of duck embryos (40 h) from four conservative flocks: KhO, A3, O1, LSA, maintained since the seventies as closed flocks. A total of 336 embryos were examined of which 27 (8%) had an abnormal chromosome complement. The frequency of embryos with chromosome abnormalities varied from 4.9% in the A3 flock to 13.7% in the LSA flock. In the two remaining flocks, (KhO and O1) the frequency was 5.9 and 6.6, respectively. Pure haploidy and haploid/diploid chimerism were the most frequently identified abnormalities in all flocks examined.