SUMMARY: Fragments of solid organs can be squashed, without destroying the viability of the cells, to form a thin sheet of cells which is stuck to polythene film with clotted mouse plasma. The film conveniently floats on a simple culture medium in which embryonic tissues multiply within 24 hr. and adult tissues survive for several days. The tissue on the polythene is thin enough to mount on a microscope slide and examine with phase-contrast illumination and an oil-immersion objective; alternatively, since the polythene is inert to most organic solvents, the tissue can be stained and mounted, using standard histological techniques. The squashed tissue on polythene is more readily infected by viruses and more easily examined than are fragments of tissue embedded in plasma on a coverglass. The method was used to study one virus cytopathogenic for many chick tissues and another virus detected by the haemadsorption phenomenon.