An RNA-synthesizing complex was found in the nucleoplasm of fowl plague virus-infected chicken fibroblast and Ehrlich tumour cells. The complex sedimented at 120 S and banded in caesium chloride at 1-39 to 1-41 g/ml. It contained an influenza nucleocapsid protein as a major protein constituent. The complex functioned late in infection, and RNA synthesis in it was resistant to actinomycin D, the properties expected of influenza virus replicative complex.