125I-LEP was prepareded by 125I with indirect iodination and direct iodination respectively to develop RIA for method comparison.For the indirect iodination

BH agent was iodinated by ch-T

then conjugated to leptin in ice bath.For the direct iodination

LEP was iodinated by ch-T with direct method.The specific radioactivity of 125I-LEP with indirect iodination was 1.43 MBq/μg

the total labeling rate of 125I was 37.8%

the sensitivity was 0.25 μg/L.The standard curve(0.5～30 μg/L) was stability with the B:B0 from 92.7%～17.5% to 94.6%～22.8% in 45 days.For the direct iodination

the specific radioactivity of 125I-LEP was 1.79 MBq/μg

the total labelling rate of 125I was 41.4%

the sensitivity was 0.37 μg/L.The standard curve(0.5～30 μg/L) was stability with the B/B0 from 87.7%～23.7% to 91.4%～35.2% in 44 days.The standard curve stability of the 125I-LEP prepared by the indirect iodination was not much better than that by the direct iodination in 45 days.They can satisfy the needs in clinic use.Which were worth of additional exploration to enhance the quality in RIA of LEP.