Objective To establish the microtiter plate radiobinding assay (RBA) of IA-2A and to evaluate its clinical application. Methods The purified ~(35)S - IA-2 was incubated with sera for 24 hours on a 96-well V-shaped bottom plate, and then transferred to the Millipore plate coated with protein A, and counted with liquid scintillation and luminescence counters after washing. The IA-2A levels were detected in 162 patients with type 1 diabetes(T1DM),210 patients with newly diagnosed type 2 diabetes(T2DM) and 224 healthy controls to evaluate clinical application of IA-2A RBA. Results 1. The intra-coefficient of variation (CV) of the assay was 4.1%～10.0%, and the inter CV was 5.7%～12.8%. 2. The results from DASP 2005 showed that the sensitivity and specificity of the assay were 72% and 98%. The results of IA-2A from two methods of RBA and classical radioligand assay(RLA) were significantly correlated (r=0.962,P＜0.001) with a consistency of 96.5%. 3. When compared with the healthy controls, T1DM patients had higher positivity for IA-2A (22.8% vs 0.89%, χ~2=49.9,P＜0.001), but no significant difference was found in T2DM patients(2.4% vs 0.89%, χ~2=1.5,P＞0.05). 4. The consistency rate of IA-2A measurement was 100% between RBA using finger tip blood and RLA using venous blood (r=0.977,P＜0.001). Conclusions The microtiter plate RBA of IA-2A using finger tip blood has high sensitivity, specificity and reproducibility, and possesses a good clinical value.