The classical procedure used for the preparation of [125I]- and [131I]metaiodobenzylguanidine (MIBG) is the solid-phase isotopic exchange between MIBG and radioiodide. This reaction requires 1.5 hours at 160 degrees C to obtain maximum total labelling yields of 75-80%. Recently, the importance of rapid procedures for the preparation of 123I-MIBG has been highlighted. A highly efficient procedure for the industrial production of 123I-MIBG using ascorbic acid, tin sulfate and copper sulfate pentahydrate in 0.01 M sulfuric acid is reported. Sequential radio-TLC analysis of the labelling mixture shows that the labelling yield reaches 98% within 45 min at 100 degrees C. The specific activity of the 123I-MIBG produced in this manner is on the order of 100 Ci/mmol.