Testosterone is the principal male sex hormone but is also present in smaller amounts in women and may be important for their health. Among its likely actions in women are the building of bone and muscle mass, increase in interest in sex (libido) and effects on the mood. Testosterone is commercially available as a hormone replacement therapy for males with an absence or lack of testosterone production. Testosterone for males is mainly given in the form of shots or skin patches which have certain disadvantages such as pain from shots and skin rashes from patches. It is anticipated that this experimental gel application will produce levels of the drug in the normal range in women.