3-Epi-Gibberellin A(63) (3-epi-GA(63)) was identified by full-scan GC-mass spectrometry of a purified extract from culture media of prothallia of the fern, Anemia phyllitidis. This is the third antheridiogen, following antheridic acid and 3 alpha-hydroxy-9,15-cycle-GA(9), in this species. 3-Epi-GA(63) showed slightly less activity than antheridic acid in antheridial formation and dark spore germination assays.