Induction of germination of Phycomyces blakesleeanus spores by a heat shock and subsequent incubation at 25 degrees C in a glucose- or 6-deoxyglucose-containing culture medium resulted in an intense (20-40 times the initial value) rise in the concentration of fructose 2,6-bisphosphate and hexose 6-phosphates. The increase in the concentration of fructose 2,6-bisphosphate but not that of hexose 6-phosphates was restricted to a 25-min period during which the spores acquired an irreversible capacity to germinate. Incubation of the spores in water for any period of time during this critical period resulted in a parallel decrease in their ability to form hexose phosphates and to germinate. A similar rise in hexose phosphate concentration was also observed when P. blakesleeanus spores were activated by incubation in the presence of acetate and also after induction of germination of other dormant (Neurospora tetrasperma) or nondormant (Mucor racemosus) fungal spores. Extracts of dormant and heat-activated P. blakesleeanus spores contain a fructose, 1,6-bisphosphatase that is inhibited by fructose 2,6-bisphosphate and AMP in a synergistic manner. They also contain a 6-phosphofructo-2-kinase and a fructose-2,6-bisphosphatase.