Arginine vasopressin (AVP) plays an important role in stress-induced activation of the hypothalamic-pituitary adrenal axis. In the present study, AVP-enhanced green fluorescent protein (eGFP) transgenic rats were used to investigate changes in AVP-eGFP expression in the hypothalamic paraventricular nucleus (PVN) and the median eminence (ME) upon exposure to stress conditions. The eGFP fluorescence in the parvocellular division of the PVN (pPVN) was markedly increased 5 days after bilateral adrenalectomy (ADX) and it was colocalised with corticotrophin-releasing hormone-like immunoreactivity in the pPVN. Peripheral administration of dexamethasone completely suppressed the increase of eGFP fluorescence in the pPVN and the external layer of the ME (eME) after bilateral ADX. Significant increases of eGFP fluorescence were observed in the pPVN 6, 12, 24 and 48 h after intraperitoneal (i.p.) administration of lipopolysaccharide (LPS). In the eME, eGFP fluorescence was significantly increased 48 h after i.p. administration of LPS. By contrast, eGFP fluorescence changed neither in the magnocellular division of the PVN, nor the internal layer of the ME after i.p. administration of LPS. Our results indicate that AVP-eGFP transgenic rats are useful animal model to study dynamic changes of AVP expression in the hypothalamus under stressful conditions.