Available androgen binding to soluble proteins from the cytosol of human endometrium was studied using the dextran coated charcoal adsorption method and sucrose density centrifugation analysis. Specific binding of [3H]-5α-dihydrotestosterone ([3H]-DHT) was observed with both methods. The apparent dissociation constant (Kα), for DHT binding is 1.3×0.2 (SEM) nM and the binding capacity 177×42 (SEM) fmol/mg protein. Sucrose density ultracentrifugation identifies specific [3H]-DHT binding that sediments at 4S and 8S. The stability of the androgen receptor in human endometrium is increased by the addition of 10% glycerol to the homogenization buffer. The addition of trypsin or pronase and heating at 60°C reduces specific binding which demonstrates that the specific [3H]-DHT binder is a protein. The uptake of [3H] DHT in endometrial tissue minces indicated that 20% of the bound radioactivity was nuclear. Steroid specificity suggests that the binding protein from the uterus is specific for androgens. These observations indicate that androgen binding protein in the human uterus has the characteristics of the androgen receptor.