Investigated mouse killing behavior in 5 experiments with male Long-Evans rats (N = 233). Hunger potentiated mouse killing by naive Ss, but not by Ss familiarized with mice before and during food deprivation. Once Ss had been made hungry, mouse killing was unaffected by increasing or decreasing severity of food deprivation or by time of testing with respect to a regular feeding hour. Ss fed either dead mice, powdered chow, or hard pellets while on cyclic food deprivation were about equally likely to kill, showing that hunger does not indirectly potentiate killing by increasing practice of responses like pouncing and biting. Whether hungry or not, killers were likely to eat their prey, whereas nonkillers were unlikely to eat the same prey. Ss killed 12-14 day-old rat pups as often as they killed mice, but killed weanling rat pups less often. Findings question several common notions regarding predatory aggression. (26 ref.) (PsycINFO Database Record (c) 2006 APA, all rights reserved)