In response to the remarks made by the two Marks on Fluo-3: The molecular probes catalogue (1992-1994) page 116 states that Calcium Green indicators are about 5 times brighter than fluo-3 at high Ca2+ levels and BLEACH at a significantly slower rate. I have used both types of indicators in crayfish motor nerve terminals and found that fluo-3 bleached so rapidly that I could not use it, whereas Calcium green worked wonderfully (Cooper et al., J. Neurosci. 15:4209-4222, 1995).