It is known that some athletes use androgenic anabolic steroids to promote skeletal muscular strength and muscle hypertrophy in response to muscle strength training. However, it is not defined whether anabolic steroids are effective for muscle hypertrophy. In order to make this question clear, we examined the conditions of a binding assay of cytosolic androgen receptor on rat skeletal muscle as the first step. We used ³H-mibolerone as the ligand for specific binding to the androgen receptor. The following conditions of the assay were examined in this study: the incubation temperature and time, concentration of ³H-mibolerone, the effects of monothioglycerol and triamcinolone acetonide, and the effect of repeated freezing and thawing of the samples on binding. It was a suitable condition for an androgen receptor assay that samples prepared from unfrozen fresh muscle were incubated with 16nM ³H-mibolerone at 4°C for 20hrs, with monothioglycerol (20mM) and triamcinolone acetonide (25μM) added. Using these assay conditions, we measured the binding capacity of androgen receptor in rat skeletal muscles. The values of K_d and B_max in M. gastrocnemius were 3.61±0.60×10^-9M and 3.18±2.23fmol/mg protein respectively.