The prey-catching behavior of ferrets (Putorius furo L.) consists mainly of instinctive behavior patterns, which can be elicited only through their releaser. Then they are performed stereotypically. To get information concerning the central background and the hierarchical structure of this behavior the neuroleptics Haloperidol (0.14 mg/kg), Clozapine (10 mg/kg) and Chlorpromazine (4 mg/kg) were injected i.m. under controlled conditions. In a conditioning experiment the reactivity of the animals was examined. This conditioned reaction was strongly decreased by the drugs. The reaction to the natural stimulus the prey was changed, but not suppressed. The modification of the predatory behavior was manifedsted in an "improvement" of orientation reactions when pursuing the prey and in a better placement of bites. This effect, most evident with Haloperidol, is possibly due to the specific neuroleptic component of the substances. A delay in approaching the prey, or even the total suppression of the prey-catching behavior is suggested to be due to a sedative component which was most obvious in some experiments with Clozapine. On the other hand, there are behavioral elements like the use of paws which are not effected by the neuroleptics. From these and other observations, it is concluded, that the predatory behavior of the ferret has a hierarchically organisated structure. Further it is suggested that some functional connected parts of the behavior have distinct central representation, for they are not influenced in the same way by these drugs.