A procedure is described which permits the simultaneous light microscopic examination of the distribution of a cellular antigen by immunofluorescence and the radioautographic determination of whether the same cell is in S phase. Cells are viewed simultaneously with epifluorescence illumination to visualize antigens and transmitted darkfield illumination to determine DNA replication. Alternatively, the same cell can be viewed first in epifluorescence and subsequently in brightfield or phase contrast to visualize radioautographic grains. The method is illustrated with antibodies to tubulin, myosin and cytochrome oxidase. Comparison of the radioautographic and immunofluorescence images demonstrates that the arrangement of cytoskeletal structure is maintained throughout interphase and is not altered during DNA replication. Immunofluorescence radioautography should be useful in any system where a comparison in individual cells between replication and the appearance, distribution or rearrangement of specific antigens is desired.