This study explored the effect of the anti-androgen spironolactone on sex-hormone binding globulin (SHBG) and the distribution of circulating testosterone (T) into various free and bound fractions in seven women with hirsutism assessed before and then monthly for three months on a regimen of spironolactone, 100 mg bid as the sole therapeutic agent. Blood samples were taken at each assessment time for a battery of androgen parameters and serum T fractions studies. None of the women were judged obese based upon body mass index values. After three months of spironolactone therapy, there was little change in the hirsutism index, and measurement of serum T, androstenedione, DHEA-S and 17 beta-estradiol showed no significant changes, the same occurring with SHBG-binding capacity. However, there was a shift in the distribution of circulating T, with a decrease in SHBG-bound T and an increase in albumin-bound and free T (non-SHBG-bound fractions). As previous reports suggest that non-SHBG-bound fractions represent bioavailable fractions, the current data suggests that T fraction studies may not be clinically useful parameters of hyperandrogenism in women receiving antiandrogen therapy.