Microdialysis methods for the quantitative determination of the extracellular concentration of neurotransmitters are described for basal and transient conditions. Measurements of dopamine (DA) in the nucleus accumbens and striatum of the rat are used as examples. The factors affecting microdialysis recovery of neurotransmitters are reviewed. Computer simulation is used to examine the effect of release and uptake on microdialysis recovery. Several new applications of microdialysis are suggested.