The compound {N-methyl-[(11)C]}2-(4'-methylaminophenyl)-6-hydroxybenzothiazole, "PIB", measured by positron emission tomography, has been demonstrated to image brain beta-amyloid deposition in Alzheimer's disease (AD). In the present study the benefit of measuring the PIB accumulation rate together with the unidirectional influx of PIB into the brain was investigated in healthy control subjects and patients with AD. In a monkey changes in the influx rate constant K(1) of PIB closely followed changes in CBF, caused by alteration of Pa(CO2). In addition, K(1) was high both in the monkey and in humans, suggesting that this parameter reflects CBF. Most AD patients studied showed clearly higher accumulation rate for PIB than the controls in cortical brain areas, while a few patients showed as low accumulation as the controls. K(1) did not correlate with the accumulation rate, indicating that K(1) for PIB provides extra information besides the accumulation rate.