HAEMAGGLUTINATION studies with arthropod-borne viruses are normally carried out using red blood cells from one-day-old chicks, although cells from mature pigeons have been used in the case of Murray Valley encephalitis virus1. An observation made in the West African Council for Medical Research Laboratories in Lagos that cells from mature ducks were agglutinated by a yellow fever antigen led to a study of readily available domestic birds. Cells from Muscovy ducks (Cairina maschatai), from a local (Badagri) variety of the domestic duck (Anas boscas) and from Chinese geese (Cygnopsis cygnoides) were compared with cells from one-day-old chicks against yellow fever, Uganda S, Zika and West Nile antigens. Goose cells gave titres which were at least as high as those obtained with chick cells, and usually higher, and the settling patterns were consistently sharp and easy to read. Duck cells, although agglutinated, gave lower titres and showed a tendency to spontaneous agglutination in controls. Goose cells were thereafter used as a routine in the Lagos laboratory, and experience over more than a year has shown them to be highly satisfactory in haemagglutination and haemagglutination-inhibition tests with the antigens already mentioned, and in addition with antigens prepared against Semliki forest, Ilheus and the Trinidad 1751 strain of dengue virus. Details of this work will be published elsewhere.