To determine whether the hormonal changes associated with the normal menstrual cycle influence FFA metabolism, FFA turnover was measured in 12 women during both the follicular (days 4-10) and luteal (days 18-24) phases of their menstrual cycles. The luteal phase was confirmed by increased serum progesterone concentrations. Overnight postabsorptive FFA flux was similar in the follicular and luteal phases of the menstrual cycle (6.9 +/- 0.8 vs. 5.8 +/- 0.5 mumol kg-1 min-1, respectively, P = NS). In addition, the FFA response to 3 h of somatostatin-induced hypoinsulinemia was virtually identical on both study days. Finally, we compared the intraindividual variability of basal FFA flux from studies performed in different vs. the same phase of the menstrual cycle; no difference was present. We conclude that the cyclic changes in estrogen and progesterone production which occur during the normal menstrual cycle appear to have minor, if any, effects on FFA mobilization.