The trial is of open label single centre design. The serum concentrations of testosterone and plasma concentrations of anastrozole will be measured in 12 premenopausal women. Participants will be stratified in a 50:50 manner in two BMI (Body Mass Index) groups, <25 and 25 kg/m2, respectively. There will be a lead group of two participants in whom the serum/plasma concentrations will be examined after the first four weeks, to determine whether the sampling schedule adequately describes the serum/plasma concentration-time profiles or should be adjusted.