Estrogens have been recognized as a major regulator of vascular tone and structure, particularly in the skin. The objective of this study was to investigate the effects of endogenous estrogens on the skin microcirculation. Skin blood flow was measured at the forearm at rest and during postischemic hyperemia using laser Doppler flowmetry in 32 healthy women (mean age 34.5 +/- 3.9 years) involved in an in-vitro fertilization program. Women were treated for 10 to 12 days with gonadotropin-releasing hormone agonist (total dose 40.3 +/- 3.3 mg) and human menopausal gonadotropin (1942 +/- 801 IE) or follicle-stimulating hormone (2544 +/- 1071 IE) according to individual estrogen levels. Plasma estrogen levels increased from 132 +/- 90 pmol/L (36 +/- 25 pg/mL) to 8471 +/- 4386 pmol/L (2308 +/- 1195 pg/mL) during treatment (P < 0.0001). Maximal hyperemic blood flow increased from 353 +/- 81% before treatment to 516 +/- 144% after hormonal stimulation (P < 0.0001), whereas basal skin flow was not altered. This study shows that endogenous estrogens enhance the postischemic hyperemic response of the skin microcirculation.