The purpose of this study was to define the vasopressin-sensitive area in the anterior hypothalamus-medial preoptic area (AH-MPOA) of the golden hamster that is involved in the expression of flank-marking behavior. Male hamsters implanted with guide cannulae stereotaxically aimed at various sites in the AH-MPOA were microinjected initially with 0.1 ng of arginine vasopressin (AVP) in a volume of 10 nl. Hamsters that flank-marked in response to these injections were subsequently microinjected into the same sites with kainic acid (0.2 µg/20 nl; n = 10) or an equal volume of 1 MNaOH as a vehicle control (n= 10). Four days later hamsters were tested for odor-induced flank marking by placing them into the recently vacated home cage of other hamsters and for flank marking in response to the microinjection of AVP. Animals treated with kainic acid exhibited significantly (p