The gibberellins are a group of terpenoid plant hormones with applications in agriculture and brewing. Present in low amounts in plants, they are abundantly produced by some strains of the ascomyceteGibberella fujikuroi.Gibberellin production in this fungus is repressed by nitrogen and, to a less extent, by glucose. A simple screening procedure has allowed a systematic search ofGibberellamutants with alterations in the gibberellin pathway. The pheno- types of these and other mutants indicate indépendant regulations for the biosyntheses of gibberellins and other terpenoids, such as carotenoids or sterols. The recent cloning of the first fungal gibberellin gene, the one coding for kaurene synthase inPhaeosphaeria, will facilitate the molecular characterization of theGibberellagenes involved in gibberellin biosynthesis.