1. Urinary kallikrein excretion was measured in healthy male subjects and in healthy pre- and post-menopausal females.
2. Urinary kallikrein excretion was shown to be constant throughout a 24 h period. Individual male subjects showed little fluctuation in urinary kallikrein excretion; within-subject variance accounted for 1.65% of the total.
3. Female subjects with ovulatory menstrual periods excreted significantly more kallikrein than post-menopausal females and males.
4. Pre-menopausal females showed a much greater within-subject variation in urinary kallikrein excretion and this could be related to the stage of the menstrual cycle, with significantly greater urinary kallikrein excretion in the luteal phase than in the follicular phase.
5. Plasma renin activity and plasma aldosterone concentration also showed a menstrual variation, with concentrations in the luteal phase being significantly higher than those in the follicular phase.
6. The rise in urinary kallikrein excretion in the luteal phase could be abolished by oral administration of the aldosterone antagonist spironolactone.
7. Urinary kallikrein excretion in post-menopausal females was similar to the range found in males, and showed no cyclic changes over a 4 week period.
8. Gender and menstrual status should be taken into account in studies of the physiological role of tissue kallikreins.