N-Succinimidyl 3-(tri-n-butylstannyl)benzoate (ATE) was radioiodinated using Iodogen as oxidant and useful conjugate S125IB of labeling proteins was obtained . ATE and Iodogen affecting labeling proteins were successfully isolated from S125IB by Sep-Pak silica . The labeling efficiency was more than 93%. Several factors affecting labeling such as labeling time

the amount of Iodogen and the mole ratio of ATE to Na125I

were studied. The better labeling conditions were obtained as follows: mole ratio of ATE to Na125I = 6:1

Iodogen=7mg

labeling time = 5min in room temperature.