Electrical Stimulation of the brains (ESB) of 63 Mallard ducks (Anas platyrhynchos) that were free to move about in a 1.5 X 1.5 X 1.5 m chamber yielded detectable responses from 416 of the 515 sites tested (286 in males, 130 in females). Responses ranged from relatively simple acts such as feather-tract movements or rapid opening and closing of the bill through prolonged oiling-preening sequences to complex attack and escape activities. Plots of histologically verified electrode locations indicated that most responses were elicited from fairly extensive and widely (but not completely) overlapping regions. All attack points were from di- and telencephalic sites while escape responses were evoked from many mesencephalic points as well. Threat sites overlapped both of these response sets and threat accompanied all attack more intense than occasional nipsor jabs at a companion. Stimulus control of the evoked responses varied from questionable increases in probability of some acts to highly repeatable actions, that commenced with latencies of a second or less, at stimulus onset and terminated promptly at the end of stimulation. In attack and escape behavior variable actions were sometimes taken to achieve similar ends. Hunger, thirst and nonagonistic social behavior were not evoked.