Having previously established that biologically active luteinizing hormone (LH) is secreted in episodic pulsations that vary in relation to the menstrual cycle, we investigated the possibility that a temporal relationship could exist between the bioactive LH pulses and progesterone secretion from the late corpus luteum. In 4 young women blood was withdrawn every 15 min for 8 h. Serum progesterone concentrations fluctuated at a mean frequency of 0.9 h with a wide range of amplitudes (13.8 to 1.7 ng/ml). Serum bioactive LH pulse frequency in contrast was 0.25 pulses/h in all subjects. The pulse amplitude was 18.2 to 12.4 mIU/ml (2nd IRP-hMG). These data reveal that within the 8 h-period studied, progesterone secretory pulses occurred four times more frequently as those for bioactive LH. Therefore it is unlikely that a temporal relationship exists between individual bioactive LH and pulses of progesterone-secreted by the late corpus luteum.