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 GA9 (4-week-old prothallia); GA9, GA24, GA25, antheridic acid and 3-epi-GA63 (6-week-old prothallia); and GA4, GA9, GA15, GA19, GA20, and GA24 [young sporophytes (younger than one year old) and/or old sporophytes (between one- and two years old). Of these compounds, GA24, GA9, and GA4 were quantified by gas chromatography-selected ion monitoring, using (2)H-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 GA24, 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 GA9, the content in young and old sporophytes being 15.3 and 7.3 ng/g fresh weight, respectively.