Upon stimulation by a steroid hormone, the glucocorticoid receptor (GR)moves from the cytoplasm to specific sites in the nucleus, but the mechanism of this transport either within the cytoplasm or within the nucleus is unknown. To address these issues, we are using a GFP-tagged GR and FRAP microscopy to study rates of transport within and between the cytoplasm and nucleus. In addition, we are constructing mutant forms of GR tagged with GFP to see what domains of the molecule are important for proper cellular localization.