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1. It is known that females have a lower skin perfusion than males. In women there are also differences in blood flow at different reproductive stages of their lives. As an initial investigation of the possible contribution of sex hormones to these differences, we studied skin and forearm blood flow during the natural changes in hormone levels which occur during the menstrual cycle. 2. Thirty-one healthy female volunteers were studied. The effect of a standardized finger cooling test (immersion of a gloved hand in a 16°C water bath) on finger skin temperature and on laser Doppler flux in the finger, and forearm blood flow (strain gauge venous occlusion plethysmography) was assessed at four different times during one cycle: during menstruation, 1 day before ovulation, 2 days after ovulation and at the mid-luteal phase. Test days were determined by daily measurements of basal body temperature and were confirmed afterwards by determinations of serum luteinizing hormone, follicle-stimulating hormone, 17β-oestradiol and progesterone. 3. Peripheral skin circulation varied significantly within one menstrual cycle. The extremes were a mean finger skin temperature of 25.9 ± 3.0°C in the luteal phase compared with 28.4 ± 3.7°C in the pre-ovulatory phase (P = 0.002). The respective values for the mean laser Doppler flux were 18.4 ± 10.9 compared with 29.2 ± 16.4 arbitrary units (P = 0.003). 4. Baseline forearm muscle blood flow also varied significantly (P = 0.04) within one menstrual cycle, with low values in the menstrual phase compared with the other phases. 5. In conclusion, we have shown that peripheral skin circulation and forearm muscle blood flow exhibit significant variability during the hormonal changes in a menstrual cycle.