Many nuclear proteins have been successfully localized using immunofluorescence microscopy. These proteins span all nuclear domains, including the nuclear envelope, nuclear lamina, nucleolus, chromatin-associated proteins, and proteins associated with RNA metabolism and nuclear bodies. This article describes a general method for localizing nuclear proteins. Cells grown on coverslips are fixed in either formaldehyde or methanol and permeabilized in Triton X-100. Incubating the cells with primary antibody and fluorescently conjugated secondary antibody allows visualization of the target antigen.