Hi, richard03, thanks for your attention. recently i got some positive results by using high concentraion of the primary AB. However, it's accompanied by high background also. certainly, this high background could be improved by reducing the concentration of secondary AB (biotinylated anti-mouse, rabbit), but then it leads to less specific staining again. I would like to post my protocol briefly for discussion: Wash by PBS--fix by acetone(4degree) 15min--0.5%H2O2/MeOH incubation--permeabilize by 0.1%Triton X-100 15min--2N HCL incubation 30min (37degree)--0.5M NaHCO3 10min--50mM Tris buffer 10min--1%BSA/3%HS 30min--primary AB 1:200 2h RT--Secondary AB (biotinylated anti-mouse, rabbit) 1:1000 1h RT--ABC kit--develop.