Amphetamines (d- at 0.5--4 mg/kg; 1- at 2--4 mg/kg) inhibited spontaneous mouse killing by some, but not all cats. Various other drugs (drugs and maximum tested doses were: imipramine, 64 mg/kg; amitriptyline, 32 mg/kg; tranylcypromine, 2 mg/kg; tripelennamine, 4 mg/kg; scopolamine, 1 mg/kg; methyl scopolamine 1 mg/kg; chlordiazepoxide 16 mg/kg; diazepam 4 mg/kg; meprobamate, 80 mg/kg; pentobarbital, 16 mg/kg; chlorpromazine, 8 mg/kg; and haloperidol, 0.5 mg/kg) did not reliably inhibit such killing. In contrast with rats, mouse killing by cats was not consistently blocked by antidepressants or amphetamines. When individual cats were inhibited, their reduction of killing seemed related to anorexia rather than to affective arousal.