In the present study we use the in vivo microdialysis sampling technique to register extracellular levels of neurotransmitters in the striatum of trained and untrained rats. We further evaluate the influence of 1 h of exercise on the striatal release of dopamine (DA), noradrenaline (NA), glutamate (GLU) and gamma-aminobutyric acid (GABA) in trained and untrained rats. Male Wistars were randomly assigned to a training or control group. The exercise training consisted of running on a treadmill for 6 weeks, 5 days week-1, with running time and speed gradually increased from 30 min at 19 m min-1 during the first week to 80 min at 26 m min-1 during the final training week. The animals of the control group were placed on the treadmill twice a week, and received a total of four 'adaptation sessions', in which they exercised 15-45 min at 26 m min-1. Brain dialysates were analysed with microbore liquid chromatography (LC), with electrochemical detection (monoamines and GABA) and fluorescence detection (GLU). Soleus citrate synthase and basal striatal concentrations of DA, NA and GLU were significantly different between the trained and control animals. Sixty minutes of exercise significantly increased extracellular DA, NA and GLU levels in both groups, but there was no statistically significant difference in the exercise-induced increase between trained and control animals. There was no statistical difference in basal or exercise-induced GABA levels between trained and control animals. The results indicate that exercise training appears to result in diminished basal activity of striatal neurotransmitters, while maintaining the necessary sensitivity for responses to acute exercise.