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This work evaluates the transcutaneous in vitro and in vivo immunization efficacy of five commercially available 5% imiquimod containing formulations. The parameters included micro- scopic analysis, rheological properties, drug permeation across synthetic membranes of molecular weight cutoff 10kDa and ablated murine skin with both 0.1 M HCl and a phthalate buffer pH 3.6 Ph.Eur./methanol 3/7 (v/v) as receiver solutions in a Franz-diffusion cell model. For in vivo formu- lation characterization, the cytotoxic T-cell activity and interferon-g production in C57BL/6 mice was determined ex vivo 24h after transcutaneous administration. OVA257264 (SIINFEKL) from chicken al- bumin served as a target antigen. Microscopic images demonstrated differences with respect to the presence or absence of crystalline API. Rheological properties point to a roughly ten-fold difference between the products at low shear rates. With regard to drug permeation across synthetic membranes, only 'Nan Bo' demonstrated equality compared with Aldara™, resulting in f1 and f2 values of 5.25 and 59.58, respectively. The drug permeation rates were maximum from Aldara™ across ablated murine skin. Furthermore, differentiation between the formulations containing crystalline and dissolved states of active imiqui- mod was possible using this model. The in vivo results yielded significant immunomodulating activities (p