The following gibberellins (GAs) and antheridiogens were identified by their mass spectra and Kovats retention indices from combined gas chromatography-mass spectrometry of purified extracts of the prothallia and sporophytes of Anemia phyllitidis, a Schizaeaceous fern: a trace amount of GA(9) (4-week-old prothallia); GA(9), GA(24), GA(25), antheridic acid and 3-epi-GA(63) (6-week-old prothallia); and GA(4), GA(9), GA(15), GA(19), GA(20), and GA(24) [young sporophytes (younger than one year old) and/or old sporophytes (between one- and two years old), Of these compounds, GA(24), GA(9), and GA(4) were quantified by gas chromatography-selected ion monitoring, using H-2-GAs as internal standards, and the content of antheridic acid, the principal antheridiogen, was evaluated by a radioimmunoassay which we have developed, The results indicate that endogenous levels of GAs and antheridiogens in prothallia began to increase rapidly between 4 and 6 weeks after sowing, the contents of antheridic acid and GA(24), the most abundant GA in 6-week-old prothallia, being 107.4 and 37.9 ng/g fresh weight, respectively, The most abundant GA in the sporophytes was GA(9), the content in young and old sporophytes being 15.3 and 7.3 ng/g fresh weight, respectively.