Gabapentin (GBP) is an anticonvulsant and is widely used in the treatment of epilepsy. In this study, GBP and an allyl derivative of GBP were radioiodinated with I-131 using the iodogen method; then their radiopharmaceutical potential in rats and rabbits was investigated. The radiochemical purity of I-131-GBP and its derivatives was determined by RTLC. The labeling yield was 95 +/- 2%. Biological evaluation was performed in normal rats and rabbits. Labeled compounds were intravenously injected into two rabbits via the ear vein after anesthetizing. The dynamic and static scintigrams were obtained using a gamma camera at different time. Then the labeled compounds were administered intravenously into the rats. The distribution was studied by counting the radioactivity in the removed organs. The results of biodistribution in the rats showed the clearance of I-131-ALGBP was faster than I-131-GBP. On the other hand, the uptake of I-131-ALGBP in the brain was higher than I-131-GBP at 60 minutes.