On the basis of metal ion requirements and sensitivity to chelators, the lag phase in the induction of amylase synthesis by gibberellic acid can be split into two parts. In the first, addition of the hormone rapidly sensitizes the tissue to irreversible inhibition by o-phenanthroline. This sensitivity persists throughout the incubation. When the tissue is incubated under temperature-stepdown conditions there is also a requirement for externally added iron from shortly after hormone addition. In the second stage, 3 to 4 h after the beginning of the lag period, the tissue shows a requirement for externally added calcium ions. The inhibition of enzyme activity by calcium deficiency occurs earlier and is much greater than would be expected if its only role is to stabilize α-amylase.