Little is known about how exogenous testosterone (T) affects the steroid profile in women. More knowledge would give the anti-doping community keys on how to interpret tests and detect doping.To investigate the steroid profile in serum and urine in young healthy women after testosterone administration.In a randomized, double-blind, placebo-controlled study, 48 healthy young women, were assigned to treatment with T cream (10 mg) or placebo (1:1) for 10 weeks. Urine and blood were collected before and at end of treatment. Serum steroids were analyzed with LC-MS/MS, and urine levels of T, epitestosterone (E) and metabolites included in the Athlete Biological Passport (ABP) were analyzed with GC-MS/MS.In serum, T and dihydrotestosterone levels increased, whereas sex-hormone-binding globulin and 17-hydroxyprogesterone decreased after T treatment as compared to placebo. In urine, T and 5α-androstanediol increased in the T group. The median T increase in serum was 5.0-fold (range 1.2-18.2) and correlated to a 2.2-fold (range 0.4-14.4) median increase in T/E in urine (rs=0.76). Only two of the 24 women receiving T reached the T/E cut-off ratio of 4, while when the results were added to the ABP, six of 15 subjects showed atypically high T/E (40%). In comparison, 22/24 women in the T group increased serum T more than 99.9% of the upper confidence limit of non-treated values.It seems as T/E ratio is not sufficient to detect exogenous testosterone in women. Serum total T concentrations could serve as a complementary marker of doping.