Various types of stressors were given to different groups of animals to examine their effects on the mesostriatal and mesolimbic serotonergic pathways. Results indicate that shock-induced fighting experience preferentially decreased serotonin (5-HT) levels in the dorsal raphe and striatum, while air puff stimulation selectively lowered 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) contents in the median raphe and hippocampus. Both immobilization and light footshock stress have a more consistent effect on both serotonergic systems. These results suggest that different stressors have differential influences upon central 5-HT neurons and, other than anatomical differentiation, these serotonergic neurons are not homogeneous with respect to their responses to stress either.