We wished to investigate if a testosterone gel administered percutaneously to postmenopausal women could result in stable serum levels of the hormone and which dose was required to produce levels within the normal premenopausal range. Fifteen postmenopausal women, mean age 55.3 years (range 45-70 years), volunteered to participate in the study and were divided into three groups. They received 10, 20 or 30 mg of testosterone as a 1% testosterone hydroalcoholic gel at 09.00 hours daily for 14 days. The gel was applied in a thin layer on the outside of the thigh each morning, over an area of approximately 15 cm². Blood samples were collected hourly between 09.00 and 17.00 hours on days 1 and 14, and also at 08.00 hours on days 3, 5, 11, 12, 13 and finally day 16, i.e. 2 days after termination of treatment. The mean basal serum level of testosterone was 1.1 ± 0.9 nmol/l and for 5-dihydrotestosterone 208 ± 143 pmol/l. There was a clear increase from the 10 mg to the 20 mg treatment (mean testosterone level during treatment 3.2 and 7.2 nmol/l, respectively) while serum testosterone values after 30 mg showed very little further increase (mean 7.5 nmol/l). Values for days 3-5 were quite similar to those for days 13-14. The present study suggests that adequate and acceptable serum levels of testosterone can be achieved with 10 mg testosterone applied transdermally.