Tissue distribution and the ability of hydrodynamically delivered GFP siRNA to silence GFP expression in GFP-transgenic mice, seen at 600 × magnification. Suppression of green fluorescent protein was seen in the liver, spleen, thymus, lung, muscle, heart, kidney (shown), brain, and Peyer patches (not shown). The qualitative change in GFP intensity and the overall number of fluorescing cells per field was made by an investigator blinded to the sample identity.