GABA is a non-protein amino acid that accumulates rapidly in plant tissues in response to biotic and abiotic stress. There have been a number of suggestions as to the role that GABA might play in plants, ranging from a straightforward involvement in N metabolism to a signal mediating plant-animal and plant-microbe interactions. It has also been several proposed that it might function as an intracellular signalling molecule in plants. Here, we discuss recent evidence that plant cells respond at the molecular level to the presence of applied GABA. We argue that these data might serve as the basis for investigating the possible signalling role for GABA in plant development and stress responses in more detail.