Ketalization of the biomolecule progesterone with (6-bromo-7-hydroxycoumarin-4-yl)ethane-1,2-diol gives the photolabile progesterone derivatives 3 and 4. These compounds display dramatically reduced bioactivity and release progesterone upon irradiation with UV/vis or IR light. In particular, 4 can be used to perform concentration-jump experiments with high temporal and spatial resolution that allows one to study elegantly the mechanisms of rapid nongenomic cellular events evoked by progesterone. The usefulness of 4 was demonstrated by measurement of changes in swimming behavior of single human sperm caused by progesterone-induced Ca(2+) influx in the sperm flagellum.