p-Chloroamphetamine (PCA), a serotonin depletor, was given to rats at least 24 h prior to testing in an open field or a shock avoidance Y-maze task. In the open field PCA groups showed hypoactivity and increased defecation up to 30 days after drug administration. These same animals plus independent groups of PCA animals, showed facilitated avoidance acquisition in the Y-maze up to 15 days after PCA administration. At the beginning of behavioral testing serotonin levels in PCA animals were reduced 70 percent and were still reduced 41 percent after 38 days in whole brain. These results suggest a separation between shock and non-shock effects of brain serotonin depletion. The facilitated avoidance also provides support for the role of serotonin as an inhibitory neurotransmitter mediating a behavioral suppression system.