Abstract This study reports the specificity, kinetics and thermodynamics of the binding of tritiated testosterone to specific receptors in the cytosol of the hypothalamic-preoptic area of the adult male mouse brain. Values for the kinetic parameters k a K D, k a, k d and the apparent free energy (ΔG o°c) are reported. The specificity of these receptors was investigated by LH-20 chromatography and sucrosegradient centrifugation. Differences in receptor specificity between the mouse and that reported for the rat are described. The effects of the antiandrogens, cyproterone acetate and BOMT, and the antiestrogens MER-25 and clomiphene citrate on the binding of tritiated testosterone to specific 8s receptors are also reported. The effect of these steroid receptor antagonists on testosterone binding is discussed in relation to the current theory on the mechanism by which androgens influence brain function.