The authors investigated whether testosterone levels and testosterone availability differ between older lean subjects with and without Alzheimer's disease (AD). Sex hormone binding globulin (SHBG) and estradiol levels were higher, whereas the free androgenization index (FAI) was lower, in lean subjects with AD than in lean subjects without AD. Factors involved in the increase of SHBG secretion could have an important role in the lower testosterone availability of subjects with AD.