A hatching technique involving biotic deoxygenation and confinement of eggs in small glass tubes is described for the tree hole mosquitoes Aedes triseriatus and Ae. hendersoni. Using this technique, 95-100% of the eggs of several geographic strains of Ae. triseriatus hatched within a 5-hr period. Similar results were obtained using Ae. hendersoni. This method is essential for critical studies of egg diapause. Results indicate that installment hatching does not occur in Ae. triseriatus when eggs are properly conditioned and are provided with an optimal hatching stimulus.