Vertebrate olfactory neurons are unique among neurons in that they are continually replaced throughout the life of the animal. The rate of neurogenesis can be regulated by manipulating the system to abbreviate or prolong the average life of a sensory neuron. Moreover, the neuron may die before or after reaching full maturity. When compared with other neurons, the fully mature olfactory neuron retains juvenile characteristics; it is probable that genetic controls operate to maintain this relatively immature state.