Gibberellins A1, A3, A4, and A7 biosynthetically labeled with 14C were added to gibberellin-producing cultures of Gibberella fujikuroi. In cultures transferred to 10% glucose solution most of the gibberellin A4 was first dehydrogenated to gibberellin A7 before being 7-hydroxylated to gibberellin A3. A small amount of gibberellin A4 was 7-hydroxylated directly to form gibberellin A1, but none of the gibberellin A1 was subsequently metabolized to gibberellin A3. In cultures growing in a medium which supported higher yields of gibberellin A1, more of the 14C-labeled gibberellin A4 supplement was directly 7-hydroxylated to this product. Gibberellin A3 was again formed mainly via gibberellin A7, but a small amount was derived by dehydrogenation of gibberellin A1. In these cultures gibberellin A4 was also metabolized to an unidentified gibberellin-like substance, probably an isomer of gibberellin A1.