Postmenopausal hormone therapy (HT) is associated with many diseases and conditions, but the underlying molecular mechanisms involved are incompletely understood. The aim of the current study was to investigate the effect of 4 types of HT on gene transcription. 24 women (6 women in 4 treatment groups) received 2 mg 17-estradiol combined with 1 mg noresthisterone acetate (NETA), 1 mg 17-estradiol combined with 0.5 mg NETA, tibolone, or raloxifene hydrochloride. RNA was isolated from whole blood before treatment (baseline) and after 6 weeks on treatment. The changes in mRNA from baseline to 6 weeks were assessed with a microarray chip.