Velocity at VO(2 max) (vV(.)O(2 max)) and peak treadmill velocity (PTV) are variables highly predictive of endurance performance. However, how these variables are affected by the menstrual cycle is unknown. The aim of this study was to assess the effect of the menstrual cycle on vV(.)O(2 max) and PTV. Ten, female runners were studied across three menstrual cycles. Training, menstrual history and mood states were assessed for 2 months, with daily salivary samples taken to detect menstrual phases. During the third menstrual cycle, participants completed a maximal test to determine V(.)O(2 max), vV(.)O(2 max) and PTV in the early follicular phase, late follicular phase, early luteal phase, late luteal phase and menses. Progesterone increased at the onset of the luteal phase [mean (SEM); 490 (73.6) pmol l(-1)] compared to the follicular phase [344.6 (59.7) pmol l(-1)). No significant differences in the psychological mood states between the phases of the menstrual cycle were found (P>0.05). No significant differences in vV(.)O(2 max) (P=0.611), or PTV (P=0.472) were found between the phases of the menstrual cycle. Thus, vV(.)O(2 max) and PTV are not affected by the monthly menstrual cycle in female endurance runners.