The recent isolation and characterization of steroid receptor coding sequences has revolutionized the field of steroid hormone action. These studies have revealed that steroid receptors are members of a much larger nuclear receptor "super family." The ligand and DNA binding domains have been shown to be molecular components that functionally interact to transform the steroid-receptor complex into a highly specific gene regulator that induces or represses the expression of cell-specific target genes. Molecular genetic approaches have been used to study structure-function relationships of several steroid receptor proteins, the most extensive analysis has been that of the glucocorticoid receptor. Several breakthroughs in the study of steroid hormone action include the construction of novel chimeric steroid receptor proteins, functional expression of steroid receptors in yeast, and the development of sensitive cloning techniques designed to isolate low abundance, hormonally regulated transcripts.