Abstract Ascorbic-acid excretion has been Summary measured daily in the first morning specimen of urine in five ovulating and five non-ovulating females who were receiving 500 mg. ascorbic acid each morning at breakfast throughout the menstrual cycle. Basal body-temperatures were taken daily before the subjects got out of bed. The ascorbic-acid excretion reached a peak and then diminished three days before ovulation. It increased at the time of ovulation. Two smaller post-ovulatory peaks also occurred. Control subjects did not show comparable fluctuations in ascorbic-acid excretion. The pattern of ascorbic-acid excretion closely resembles the excretion of luteinising hormone at the time of human ovulation.