Fluctuations in female sex hormones may be responsible for the high prevalence of Raynaud's phenomenon (RP) observed in premenopausal women. These hormones are known to act on central and peripheral thermoreceptors. In an attempt to establish whether cold sensitivity is altered during the menstrual cycle 50 premenopausal women were investigated. Of these, 26 had primary RP and 24 acted as controls. Each subject was exposed to environmental heating and cooling at three stages of the menstrual cycle to coincide with peaks and troughs in hormone levels. These stages were menstruation, periovulation, and during the midluteal phase. Finger hemodynamics was assessed by means of venous occlusion strain gauge plethysmography and fingertip temperature. Core temperature was assessed with an oral thermocouple. The results show that cold sensitivity was altered during the menstrual cycle in both groups with the fastest finger rewarming pattern during menstruation. Moreover, a significant difference was observed in core temperature between the two groups during the midluteal phase. As a group, subjects with RP failed to show a significant rise in core temperature following ovulation. The authors conclude that the menstrual cycle is associated with changes in the effect of cold on digital blood flow.