The aims of this investigation were to develop a no-carrier-added (nca) synthesis of (4-[18F]-fluoro-3-iodobenzyl)guanidine ([18F]FIBG) and to evaluate its potential as an MIBG analogue useful for positron emission tomography. [18F]FIBG was prepared in four steps starting from 4-cyano-2-iodo-N,N,N-trimethylanilinium trifluoromethanesulfonate in 5% decay-corrected radiochemical yield in a total synthesis time of 130 min. The specific activity was more than 1500 Ci per mmol. In vitro binding studies showed that the percent binding of [18F]FIBG to SK-N-SH human neuroblastoma cells remained constant over a 3-log activity range and was similar to that of nca [131I]MIBG. Specific and high uptake of FIBG was also seen in mouse heart and adrenals. The in vitro and in vivo properties of [18F]FIBG suggest that this compound may be a useful positron-emitting analogue of MIBG. © 1994 American Chemical Society.