Traditionally, cellular differentiation is thought to be an irreversible commitment to a given cell identity. So, for example, differentiated neurons cannot generate new cells or adopt new identities. Now, however, Melissa Wright and colleagues provide evidence for the transdifferentiation of dorsal root ganglia (DRG) sensory neurons in zebrafish larvae (see p. 3047). Using time-lapse microscopy, the researchers track DRG neurons in wild-type zebrafish and in zebrafish mutant for the nav1.6 voltage-gated sodium channel. Some DRG neurons migrate ventrally from their normal position and then adopt a phenotype characteristic of sympathetic neurons in both types of larvae, they report, but more DRG neurons transdifferentiate in the mutant larvae. Furthermore, although the loss of sodium channel expression promotes the migration of DRG neurons, once in a new environment, these neurons transdifferentiate regardless of sodium channel expression. Thus, the researchers conclude, differentiated sensory neurons retain the plasticity needed to transdifferentiate when challenged by a new environment, a finding that suggests new strategies for the treatment of nervous system diseases.