There were four phlebotomies performed for each subject. Blood was drawn on menstrual cycle day 18 to 21 prior to the study, within 4 days of either the last pill or removal of the last patch, and on cycle day 18 to 21 in the second month of the washout period. Blood was collected using standardized methods with minimal stasis into vacutainer tubes, immediately placed on ice and centrifuged at 4oC. Plasma and serum was stored at -70oC until completion of the study.