Arginine vasopressin (AVP) in the CSF has been implicated in the control of intracranial pressure (ICP) and studies have shown that some patients with raised ICP also have elevated levels of AVP in their CSF. Evidence suggests that central AVP has a separate origin and may exert different effects than AVP in the peripheral circulation. The purpose of this study was to compare the effects of intracerebro ventricular (ICV) and intravenous (IV) injection of AVP on ICP and arterial BP. AVP was administered to anaesthetized, ventilated, S/D rats following a 30 min baseline recording period. BP and ICP were recorded continuously for 40 min post-injection. A single ICV injection of 0.125 microgram or 0.5 microgram AVP significantly (p < 0.05) reduced ICP from 5-26% or 0.2-1.0 mmHg for the duration of the recording period. This was accompanied by a corresponding increase in arterial BP of 5-44% or 4-34 mmHg. In contrast, iv injection of 4 ng or 0.05 microgram AVP produced an abrupt but transient rise in BP of 9-171 mmHg accompanied by a 5-23% increase in ICP. Intravenous injection of 0.125 microgram AVP increased BP to 156-171 mmHg exceeding the autoregulatory range and because of this ICP also increased significantly. BP and ICP exhibited a negative linear relationship following ICV administration of both doses of AVP but only after administration of the smaller dose iv. Vehicle alone administered by either route produced no significant changes in ICP of BP.(ABSTRACT TRUNCATED AT 250 WORDS)