Multiplication of human adenovirus type 6 was demonstrated in established cultures of bovine cells. The virus replicated, producing characteristic cytopathic effects and undiminished infectivity, through six serial passages. By means of light and electron microscopy the appearance of viral inclusion bodies were comparable to those routinely observed in infected human cells. Intranuclear paracrystalline formations were also observed in the present virus–host system. The pathogenicity and host range of human adenovirus type 6 in relation to these properties of other adenoviruses were discussed.