The development of a tomographic method of measuring regional cerebral blood flow, based on positron-emission tomographic determination of the regional cerebral kinetics of fluoromethane (F-18) (methyl fluoride) is reported. The high Ostwald solubility of fluoromethane has allowed development of a blood-flow method that takes advantage of the decades of previous blood-flow investigations with inert tracers, yet provides tomographic determinations at a spatial resolution approaching those of methods based on regional tissue deposition of radioactivity. Refinements of the method are proceeding and with a variety of clinical and research applications.