Measurement of cerebral blood flow (CBF), cerebral blood volume (CBV), cerebral oxygen extraction fraction (OEF) and cerebral metabolic rate of oxygen (CMRO(2)) by positron emission tomography (PET) with oxygen-15 labelled carbon dioxide (C(15)O(2)) or (15)O-labelled water (H(2)(15)O), (15)O-labelled carbon monoxide (C(15)O) and (15)O-labelled oxygen ((15)O(2)) is useful for diagnosis and treatment planning in cases of cerebrovascular disease. The measured values theoretically depend on various factors, which may differ between PET centres. This study explored the applicability of a database of (15)O-PET by examining between-centre and within-centre variation in values. Eleven PET centres participated in this multicentre study; seven used the steady-state inhalation method, one used build-up inhalation and three used bolus administration of C(15)O(2) (or H(2)(15)O) and (15)O(2). All used C(15)O for measurement of CBV. Subjects comprised 70 healthy volunteers (43 men and 27 women; mean age 51.8+/-15.1 years). Overall mean+/-SD values for cerebral cortical regions were: CBF=44.4+/-6.5 ml 100 ml(-1) min(-1); CBV=3.8+/-0.7 ml 100 ml(-1); OEF=0.44+/-0.06; CMRO(2)=3.3+/-0.5 ml 100 ml(-1) min(-1). Significant between-centre variation was observed in CBV, OEF and CMRO(2) by one-way analysis of variance. However, the overall inter-individual variation in CBF, CBV, OEF and CMRO(2) was acceptably small. Building a database of normal cerebral haemodynamics obtained by the(15)O-PET methods may be practicable.