Many psychoactive drugs influence the transport of neurotransmitters across biological membranes, suggesting that the physiological regulation of neurotransmitter transport might contribute to normal and perhaps abnormal behaviour. Over the past few years, molecular characterization of the neurotransmitter transporters has enabled investigation of their subcellular location and regulation. The analysis of location suggests that membrane trafficking has an important role in the normal function of these proteins. One of the major regulatory mechanisms also involves changes in localization that might contribute to synaptic plasticity. This article discusses recent work on the membrane trafficking of neurotransmitter transporters and its role in regulating their activity.