Testosterone is secreted into saliva. In saliva, testosterone is not bound to proteins. Thus concentration of testosterone in saliva is quite close to the serum free testosterone level. Currently serum free testosterone is measured by a convenient method in Japan, that reflects only 10% of the correct values. However, the correct measurement of serum free testosterone is quite costly. Collection of saliva is not invasive to subjects, and it can be done without paramedicals. Besides it is relatively cheaper. Acquisition of samples in multiple occasions is possible. These advantages of utilizing saliva will introduce the measurements of salivary testosterone in cohort studies or screening of low testosterone levels in the community.