Effects of phencyclidine (PCP) on shock-induced and spontaneous aggression in the squirrel monkey were determined. The delivery of response-independent, fixed-time (4', S-S interval) electric shock to the tail of a restrained squirrel monkey generated post-shock, hose-bite attack responses and pre-shock lever press non-attack responses. In a separate procedure shock was not delivered and spontaneous aggression responses were measured. A PCP dose response function (0.01-1.0 mg/kg SC) was determined for each procedure. In the shock-induced aggression procedure initial increases in attack were observed but upon a second determination of the dose effect curve this effect decreased and an increase in non-attack was noted. PCP produced increases in non-attack responding at high dosages in the spontaneous aggression procedure.