Body composition and its relationship with intra-arterial pressure, fluid volume partitions and oxygen consumption were studied in male rats four months following ventromedial hypothalamic (VMH) destruction during the static phase of the development of obesity. Compared with sham-operated controls, rats with VMH lesions had a greater body weight which was related to an increased body lipid content and an elevated arterial pressure and total peripheral resistance. Fluid volume distribution was normal and total body oxygen consumption (per unit of body weight) was reduced. Bilateral destruction of the ventromedial hypothalamus was confirmed in each of the rats studied and no relationship could be demonstrated between the lesion size and the magnitude of haemodynamic changes. It is concluded that the increased arterial pressure observed in obese VMH lesioned rats was directly related to an elevated total body lipid content.