Haemodynamic and metabolic sequences were investigated in nine patients having subarachnoid haemorrhage (SAH) up to 3 months following aneurysmal rupture, using positron emission tomography (PET). In the pre-spasm stage (2-4 days after SAH) cerebral blood flow (CBF, ml/100 ml/min) was 45 +/- 11, the cerebral metabolic rate of oxygen (CMRO2, ml/100 ml/min) was 2.68 +/- 0.50, and cerebral blood volume (CBV, ml/100 ml) was 5.5 +/- 1.2. CBF within the normal range and a relatively low CMRO2, indicated relative hyperaemia. This was possibly due to the direct toxic effect of SAH on the brain metabolism. CBV was considerably elevated. The spasm stage (6-15 days after SAH) showed CBF values of 39 +/- 7, CMRO2 values of 2.42 +/- 0.50, and CBV values of 5.4 +/- 1.7. CBF decreased significantly (p less than 0.05 vs pre-spasm stage), and CMRO2 also tended to decrease, while they were coupling. It is likely that this may have been induced by vasospasm. Thereafter, the PET parameters normalized gradually. During all the stages studied, significant laterality of the PET parameters was not observed. This may be because SAH and vasospasm provide diffuse pathophysiological conditions for the entire brain and cerebral arteries.