This is the first attempt to elucidate the direct effect of acupuncture stimulation on plasma levels of LH, FSH, progesterone and esterone and estradiol in normally ovulating women. Four loci, which are known from experience to relate closely to female reproductive organs, were needled with electric stimulation and the responses to synthetic LH-RH with and without acupuncture stimulation were also analyzed in the same cases. Plasma hormone levels were measured by specific radioimmunoassay. All cases showed normal responses to LH-RH corresponding to the day of the menstrual cycle. During the initial part of stimulation, both progesterone and estradiol levels rose in follicular cases and declined in luteal cases. Plasma LH levels declined and FSH showed no change at this time. The analysis of plasma LH responses to LH-RH under acupuncture stimulation revealed extraordinary re-elevation in some cases. It is suggested that properly performed acupuncture stimulation might affect the female endocrine function.