1. The response of active and inactive plasma renin to orthostasis and frusemide and to inhibition of prostaglandin synthesis by indomethacin was tested in normal human volunteers.
2. Active renin increased by orthostasis and frusemide and decreased by indomethacin. The latter also blunted the increase of active renin after stimuli.
3. Inactive renin was slightly increased by orthostasis, but was not significantly influenced by acute administration of frusemide or inhibition of prostaglandin synthesis by indomethacin.
4. The results show differences in the response of active and inactive renin to stimuli and suppression. Opposite changes of active and inactive renin were not observed in the experimental conditions studied.