A crude cytoplasmic androgen receptor preparation of rat livers or its partially purified one by a 30% ammonium sulfate precipitation was prelabeled with [3H] testosterone ([3H]T) and then incubated with nuclei from rat livers at 30 degrees C for 30 min. The formations of the [3H]T-cytosol receptor complex and its nuclear bound complex were determined. The formation of testosterone-cytosol receptor complex was a prerequisite for the nuclear binding of testosterone. Nuclear fraction, when incubated with the prelabeled crude cytosol, bound [3H]T-receptor complex as much as when incubated with the prelabeled partially purified cytosol. The addition of unlabeled crude cytosol to the prelabeled partially purified cytosol increased the nuclear binding of the receptor. The presence of a thermostable, low molecular inhibitor and a thermolabile, macromolecular activator in the crude cytosol preparation was suggested by dialysis, heating and gel chromatography.