Stimulation of dopamine D1-receptors by SKF 82958 increased extracellular neurotensin (NT) levels in the striatum and nucleus accumbens as measured by in vivo microdialysis while blockade of D1-receptors had no effect. Antagonism of NMDA receptors with MK 801 completely prevented the increased NT release induced by D1-stimulation in both structures. Tissue content of striatal NT anterior and posterior to the microdialysis probe was oppositely altered by D1-stimulation: increases were observed in the anterior striatum with decreased NT levels in the posterior striatum.